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Showing papers in "Experimental Brain Research in 1981"


Journal ArticleDOI
TL;DR: Human subjects were instructed to point one hand to different visual targets which were randomly sequenced, using a paradigm which allowed two degrees of freedom, and trajectories of the hand in space were observed.
Abstract: Human subjects were instructed to point one hand to different visual targets which were randomly sequenced, using a paradigm which allowed two degrees of freedom (shoulder, elbow). The time course of the hand trajectory and the joint angular curves were observed. The latter exhibited patterns which change markedly for different movements, whereas the former preserve similar characteristics (in particular, a single peaked tangential velocity curve). The hypothesis is then formulated that the central command for these movements is formulated in terms of trajectories of the hand in space.

1,619 citations


Journal ArticleDOI
TL;DR: The connections of the rostralmost part of the cingulate gyrus resemble the efferent cortical connectional patterns described for lateral prefrontal and orbito-frontal cortex, whereas the projections of areas 24 and 23 are directed to the neocortical, the paralimbic and the limbic areas.
Abstract: Efferent cortical connections of the cingulate gyrus are investigated in rhesus monkey using autoradiographic technique. The results indicate that the rostralmost part of the cingulate gyrus (area 32) sends projections to the lateral prefrontal and midorbitofrontal cortex and to the rostral portion of the superior temporal gyrus. In contrast, the other two major subdivisions of the cingulate gyrus, areas 24 and 23, have widespread connections within the cortex. Area 24, for example, projects to the pre-motor region (areas 6 and 8), the fronto-orbital cortex (area 12), the rostral part of the inferior parietal lobule, the anterior insular cortex, the perirhinal area and the laterobasal nucleus of amygdala. Area 23, likewise, sends its connections to the dorsal prefrontal cortex (areas 9 and 10), the rostral orbital cortex (area 11), the parieto-temporal cortex (posterior part of the inferior parietal lobule and the superior temporal sulcus), the parahippocampal gyrus (areas TH and TF), the retrosplenial region and the presubiculum. It seems that the connections of the rostralmost part of the cingulate gyrus resemble the efferent cortical connectional patterns described for lateral prefrontal and orbito-frontal cortex, whereas the projections of areas 24 and 23 are directed to the neocortical, the paralimbic and the limbic areas.

485 citations


Journal ArticleDOI
TL;DR: Receptive field size and magnification have been studied in striate cortex of awake, behaving rhesus monkeys at visual eccentricities and it is found that a point of light projected onto foveal retina is “seen” by larger numbers of striate cortical cells than a point that is projected onto peripheral retina.
Abstract: Receptive field size and magnification have been studied in striate cortex of awake, behaving rhesus monkeys at visual eccentricities in the range of 5–160 min. The major findings that emerge are (1) magnification in the foveola achieves values in the range of 30 mm/deg, (2) mean field size is not proportional to inverse magnification in contrast with previous reports, and (3) the product, magnification X aggregate field size, is greater in central vision than in peripheral vision. Thus, a point of light projected onto foveal retina is “seen” by larger numbers of striate cortical cells than a point of light projected onto peripheral retina. Implications of these findings for visual localization and two-point discrimination are discussed.

448 citations


Journal ArticleDOI
TL;DR: The results indicate that approximately 70% of the cholinergic innervation in the frontoparietal cortex is derived from acetylcholinesterase positive neurons in the peripallidal nucleus basalis, whereas the remainder appears to be localized in cortical intrinsic neurons.
Abstract: Electrothermic lesion of the peri-pallidal region of the rat caused a marked reduction in the activity of choline acetyltransferase in the ipsilateral fronto-parietal cortex without affecting the activity of glutamate decarboxylase Only lesions that involved the ventral globus pallidus significantly reduced cortical choline acetyltransferase activity; and lesions limited to the thalamus, internal capsule, pyriform cortex or zone incerta were ineffective Excito-toxin lesions of the ventral globus pallidus caused 45-5% reductions in all presynaptic markers for cholinergic neurons but did not significantly decrease presynaptic markers for noradrenergic, serotonergic or histaminergic neurons in the cortex The maximal reductions in cortical choline acetyltransferase activity achieved with the pallidal lesion was 70%; and enzyme activity reached its nadir by four days after placement of the lesion The pallidal lesion, which ablated the large isodendritic acetylcholinesterase positive neuronal perikarya, resulted in a profound loss in histochemically stained acetylcholinesterase-reactive fibers in the fronto-parietal cortex but not in the cingulate, pyriform and occipital cortex or hippocampal formation; analysis of the subregions in choline acetyltransferase activity The kainate lesion of the parietal cortex to ablate intrinsic neurons did not reduce the activity of tyrosine hydroxylase, a marker for noradrenergic terminals, but depressed glutamate decarboxylase by 68%; in contrast choline acetyltransferase activity fell only 29% The results indicate that approximately 70% of the cholinergic innervation in the fronto-parietal cortex is derived from acetylcholinesterase positive neurons in the peripallidal nucleus basalis, whereas the remainder appears to be localized in cortical intrinsic neurons

435 citations


Journal ArticleDOI
TL;DR: Stimulating electrodes were chronically implanted in the ventral hippocampal commissure and the entorhinal cortex or angular bundle of rats and the data is consistent with most of them being inhibitory interneurons, but this is not established.
Abstract: Stimulating electrodes were chronically implanted in the ventral hippocampal commissure and the entorhinal cortex or angular bundle of rats. Moveable metal microelectrodes which could be passed through the hippocampus were implanted. All hippocampal units were classified s complex-spike cells or theta cells on the basis of the form of their action potentials and their rates of firing in various behaviors. Field potentials and unit firing evoked from the stimulating electrodes were recorded during slow wave sleep. Complex-spike cells (1) could often be antidromically activated in CA3 (it was not attempted in CA1); (2) could only be induced to fire one or two action potentials in response to a single stimulus; (3) had action potentials at the same time as the local population-spike and, in condition-test studies, were depressed when the population-spike was depressed. (The population-spike is presumably the summed synchronous action potentials of pyramidal cells.) Theta cells: (1) were antidromically activated in only one out of 25 cases; (2) usually could fire long bursts of action potentials in response to a sufficiently intense single stimulus; (3) this firing occurred before, during, and after the local orthodromic population-spike. Most complex-spike cells in Ammon's horn must be pyramidal cells (projection cells), and vice versa. The case for theta cells is more difficult. Some are non-pyramidal cells with locally ramifying axons, but at least some are projection cells. The data is consistent with most of them being inhibitory interneurons, but this is not established.

384 citations


Journal ArticleDOI
TL;DR: Above threshold, the response amplitude usually increased linearly with contrast until it began to saturate at the highest contrasts, and the variance of the response increased with its amplitude; this finding perhaps underlies the Weber-Fechner relation for psychophysical contrast discrimination.
Abstract: For neurones in the cat's striate cortex, we examined the dependence of response on the contrast of moving sinusoidal gratings. Most neurones showed a clear threshold contrast below which no response was elicited. Such thresholds presumably contribute to the animal's behavioural threshold, which should not be accounted for solely in terms of the detection of a signal in the presence of spontaneous “noise”. Above threshold, the response amplitude usually increased linearly with contrast until it began to saturate at the highest contrasts. The variance of the response increased with its amplitude; this finding perhaps underlies the Weber-Fechner relation for psychophysical contrast discrimination.

267 citations


Journal ArticleDOI
TL;DR: Evidence is presented that the early low threshold effects, facilitatory for synergistic and inhibitory for antagonistic motoneurone pools, are due to stimulation of Ia fibres, while the subsequent opposite effects which had a slightly higher threshold are Ib in origin.
Abstract: Variations in the H-reflex of soleus, tibialis anterior, quadriceps and short head of biceps femoris muscles were studied in normal man, preceded by a conditioning stimulus applied to either gastrocnemius medialis, the inferior branch of soleus or the common peroneal nerve. The observed variations were evoked by low threshold afferents, had a very short latency suggesting oligosynaptic linkage and disappeared during a selective ischaemic blockade of group I fibres; they were therefore regarded as due to group I fibre stimulation. Biphasic variations were observed in almost all cases: evidence is presented that the early low threshold effects, facilitatory for synergistic and inhibitory for antagonistic motoneurone pools, are due to stimulation of Ia fibres, while the subsequent opposite effects which had a slightly higher threshold are Ib in origin. Even though the pattern of projections of group I fibres from ankle flexors and extensors is qualitatively the same in normal man as in the spinal cat, large quantitative differences are observed: in normal man the effects of group I fibres from ankle flexors and extensors upon close synergistic and direct antagonistic motoneurone pools are weak, and often negligible, whereas they are extremely potent upon quadriceps motoneurones.

265 citations


Journal ArticleDOI
TL;DR: The relationship between the variance and mean rate of discharges of simple cells in the cat striate cortex has been examined when mean rate was varied by changing either stimulus spatial frequency or contrast; the relation was roughly linear.
Abstract: The relationship between the variance and mean rate of discharges of simple cells in the cat striate cortex has been examined when mean rate was varied by changing either stimulus spatial frequency or contrast. In both cases, the variance was related to the mean discharge rate by an exponent of about 1.15; the relation was thus roughly linear. The discharge variance was on average 1.7 times the mean rate for data obtained from measurements of the neurones' spatial frequency tuning curves, and 1.48 times the mean for data from the response-contrast determination. However, this difference was not statistically significant.

251 citations


Journal ArticleDOI
TL;DR: This study contrasts the properties of compensatory postural adjustments in response to movements of the support surface with those of reaction-time voluntary movements in human subjects and finds a system which classifies movements by function, as either stabilizating or orientational adjustments, to be more useful.
Abstract: This study contrasts the properties of compensatory postural adjustments in response to movements of the support surface with those of reaction-time voluntary movements in human subjects. Subjects stood upon a six degrees-of-freedom movable platform and performed tone and movement-triggered voluntary sways about the ankle joints both under conditions of postural stability and instability. These triggered movements could be executed as rapidly as postural adjustments to support surface perturbations (80–120 ms), but only when the former were well practiced, single-choice (direction) and were performed under conditions of postural stability. Evaluation of the properties of postural adjustments and reaction-time voluntary movements revealed a number of clear organizational differences between the two categories of movement, but most interesting was the finding that, when reaction-time movements were triggered by or at the onset of platform movement, the postural adjustment always occurred first. Only when subjects were given a tone trigger 50 ms in advance of platform movement were they able to execute the reaction-time movement first. We found that the dichotomous voluntary/reflexive classification of movements was not consistent with all of the identified properties of postural adjustments and reaction-time movements. Instead, we find a system which classifies movements by function, as either stabilizating or orientational adjustments, to be more useful. In the context of whole-body movement then, intentional focal components would be closely associated with others directed towards postural stabilization.

246 citations


Journal ArticleDOI
TL;DR: It is postulated that the C3-C4 PNs can transmit to forelimb motoneurones the command for target-reaching but not for food-taking, which depends on direct activation of neuronal networks within the forelimB segments from the cortico- and/or rubrospinal tracts.
Abstract: SummaryThe purpose of this study was to elucidate the relative role of the C3-C4 propriospinal neurones (PNs) and of neuronal networks within the forelimb segments for precise forelimb movements.The effects of different spinal cord lesions were investigated on the ability of cats to retrieve food with the forelimb from the bottom of a narrow horizontal or vertical tube. The test movements, which are known to depend on the cortico- and/or rubrospinal tracts (Gorska and Sybirska 1980a, b), are subdivided into the target-reaching movement by which the paw is brought in contact with the food, and the food-taking movement, consisting of toe grasping and paw supination which are components of the movement by which the cat brings the food to the mouth.The following lesions were made ipsilaterally to the tested limb:1.A dorsal lesion in C5 interrupting the cortico- and rubrospinal input to the forelimb segments (four cats).2.A dorsal lesion in C2 interrupting the cortico- and rubrospinal input to the C3-C4 PNs and the forelimb segments (four cats).3.A ventral lesion in C5 interrupting the descending axons of the C3-C4 PNs and bulbospinal fibres to forelimb segments (three cats).4.A ventral lesion in C2 interrupting bulbospinal fibres and ascending collaterals from the C3-C4 PNs (two cats).5.A ventral lesion in C2 and a dorsal lesion in C5 sparing the cortico- and rubrospinal input to the C3-C4 PNs and their axons to the forelimb segments (one cat).6.Hemisection in C2, except the dorsal column (two cats). Severe short-term impairment of the food-taking movement was observed after lesion 1, 2, 5, or 6, but not after lesion 3 or 4. The target-reaching movement was severely impaired after lesion 2, 3, or 6 but not after lesion 1, 4, or 5. The defect after lesion 3 was not in the lifting of the limb but in the appearance of gross ataxia in aiming at the target with the paw.It is postulated that the C3-C4 PNs can transmit to forelimb motoneurones the command for target-reaching but not for food-taking, which depends on direct activation of neuronal networks within the forelimb segments from the cortico- and/or rubrospinal tracts.Long-term recovery of the limb lifting in the target-reaching movement occurred after all lesions. A partial recovery of the food-taking movement occurred after lesions 1 and 2 but not after lesions 5 and 6 which also included the ventral part of the lateral funicle; the recovery is assumed to depend on reticulospinal control of networks within the forelimb segments.

238 citations


Journal ArticleDOI
TL;DR: A parallel channel linear model is proposed which has separate visual and Vestibular pathways summing in a complementary manner, and a dual-input describing function analysis supports the complementary model; vestibular cues dominate sensation at higher frequencies.
Abstract: Measurements are made of manual control performance in the closed-loop task of nulling perceived self-rotation velocity about an earth-vertical axis. Self-velocity estimation is modeled as a function of the simultaneous presentation of vestibular and peripheral visual field motion cues. Based on measured low-frequency operator behavior in three visual field environments, a parallel channel linear model is proposed which has separate visual and vestibular pathways summing in a complementary manner. A dual-input describing function analysis supports the complementary model; vestibular cues dominate sensation at higher frequencies. The describing function model is extended by the proposal of a non-linear cue conflict model, in which cue weighting depends on the level of agreement between visual and vestibular cues.

Journal ArticleDOI
TL;DR: An analysis has been made of the ascending projection to the lateral reticular nucleus (LRN) from the previously described C3-C4 “propriospinal” neurones (PNs) which are monosynaptically activated from several higher motor centres and project caudally, some of them directly to forelimb motoneurones.
Abstract: SummaryAn analysis has been made of the ascending projection to the lateral reticular nucleus (LRN) from the previously described C3-C4 “propriospinal” neurones (PNs) which are monosynaptically activated from several higher motor centres and project caudally, some of them directly to forelimb motoneurones (Illert et al. 1977, 1978).Extra- and intracellular recording was made from cells in the C3-C4 segments which could be antidromically activated both from the lateral funicle in C7 and from the ipsilateral LRN. The ascending projection to LRN was found in 84% of the PNs terminating rostral to Th9 but at the most in 11% of the PNs projecting beyond Th9. Threshold mapping in and around the LRN showed that the stem axons of the ascending collaterals enter the nucleus from a position dorsomedial to its caudal part and terminate at different levels, along the entire rostrocaudal extent of the nucleus. Termination was not restricted to the forelimb region (the A-zone, Clendenin et al. 1974a) but was found also in the ventral part of the LRN. The conduction velocity was generally slower in the ascending than in the descending branch (mean values 26 and 44 m/s). The conduction velocity was higher in the PNs projecting beyond Th9 (mean value 101 m/s).Stimulation in the LRN evoked large monosynaptic EPSPs in forelimb motoneurones as would be expected from the double projection of C3-C4 PNs. These EPSPs are elicited from the regions where the collaterals from C3-C4 PNs ascend and terminate. Their latency and time course are those expected for EPSPs mediated by the bifurcating axons of C3-C4 PNs. It is concluded that they are produced by antidromic activation of ascending neurones also projecting to forelimb motoneurones. The monosynaptic EPSPs from the LRN were found in all motor nuclei tested but were larger in motoneurones to elbow flexors than to elbow extensors (mean values 4.5 and 2.9 mV). Motoneurones classified as fast or slow from the duration of the afterhyperpolarization received EPSPs from the LRN even if pyramidal volleys evoked excitation in the former and inhibition in the latter. Double stimuli in the LRN revealed considerable frequency potentiation of the EPSPs.Stimulation in the LRN gives marked facilitation of transmission in the reciprocal Ia inhibitory pathway to motoneurones. The effective LRN region, threshold strength and time course is the same as for the monosynaptic EPSPs in motoneurones. The Ia inhibitory interneurones receive a direct projection from C3-C4 PNs (Illert and Tanaka 1978) and it is postulated that these PNs also have an ascending collateral to the LRN which antidromically mediate monosynaptic excitation to the Ia inhibitory interneurones.It is suggested that the ascending collaterals are a link in an intrinsic feed-back by which the brain controls how the C3-C4 PNs govern forelimb movements. This mode of ascending information — a mirror of the activity reaching forelimb motoneurones and Ia inhibitory interneurones — is discussed in relation to the more complex information in other ascending systems signalling intrinsic spinal activity.

Journal ArticleDOI
TL;DR: These results are consistent with the hypothesis that the poor choice accuracy in the elevated radial arm maze task arose because of the working memory requirements of that task, rather than its cognitive mapping characteristics, and support interpretations of hippocampal function that emphasize memory processing.
Abstract: The hippocampus has been implicated as a brain structure necessary for normal memory functions and normal spatial behavior. Both these explanations are consistent with the results of previous experiments demonstrating an impairment of choice accuracy following fimbria-fornix lesions on an elevated radial arm maze because the test procedure required working memory and permitted cognitive mapping. In the present experiment, rats were tested in an enclosed radial arm maze in which each arm had a distinctive set of discriminative stimuli and the test procedure required working memory but prevented cognitive mapping. Rats were tested preoperatively, given fimbria-fornix lesions, and then tested postoperatively. The rats with lesions performed at chance levels and showed no evidence of recovery of function. These results are consistent with the hypothesis that the poor choice accuracy in the elevated radial arm maze task arose because of the working memory requirements of that task, rather than its cognitive mapping characteristics, and support interpretations of hippocampal function that emphasize memory processing.

Journal ArticleDOI
TL;DR: The direction selectivity and ocular dominance of the NOT system as a whole can provide a possible explanation for the directional asymmetry in the cat's optokinetic nystagmus when only one eye is stimulated.
Abstract: All cells in the nucleus of the optic tract (NOT) of the cat, that Bcould be activated antidromically from the inferior olive, were shown to be direction-specific, as influenced by horizontal movements of an extensive visual stimulus. Cells in the left NOT were activated by leftward and inhibited by rightward movement, while those in the right NOT were activated by rightward and inhibited by leftward movement. Vertical movements did not modulate the spontaneous activity of the cells. The mean spontaneous discharge rate in 50 NOT cells was 30 spikes/s. This direction-specific response was maintained over a broad velocity range ( 100 °/s). Velocities over 200 °/s could inhibit NOT cells regardless of stimulus direction. All cells in the NOT were driven by the contralateral eye, about half of them by the ipsilateral eye also. In addition, activation through the contralateral eye was stronger in most binocular units. Binocular cells preferred the same direction in the visual space through both eyes. An area approximately corresponding to the visual streak in the cat's retina projected most densely onto NOT cells. This included an extensive ipsilateral projection. No clear retinotopic order was seen. The most sensitive zone in the very large receptive fields (most diameters being >20 °) was along the horizontal zero meridian of the visual field. The retinal input to NOT cells was mediated by W-fibers. The striking similarities between the input characteristics of NOT-cells and optokinetic nystagmus are discussed. The direction selectivity and ocular dominance of the NOT system as a whole can provide a possible explanation for the directional asymmetry in the cat's optokinetic nystagmus when only one eye is stimulated.

Journal ArticleDOI
TL;DR: Cells located in the banks of the arcuate sulcus at its curvature changed their activity during the period in which the monkey saw a food reward in a certain position, but before it moved to retrieve the reward.
Abstract: Neuron activity was recorded in monkey cerebral cortex during a visually guided reaching task. Cells located in the banks of the arcuate sulcus at its curvature changed their activity during the period in which the monkey saw a food reward in a certain position, but before it moved to retrieve the reward. A role of these neurons in visual guidance of arm and hand movements is postulated.

Journal ArticleDOI
TL;DR: The hypothesis is put forward that the vestibular nuclei and the flocculus behave in a complementary fashion in processing visual-vestibular information, theFlocculus being specialized for high velocity optokinetic nystagmus and suppression of Vestibular nyStagmus.
Abstract: The activity of Purkinje cells (P-cells) was recorded in the flocculus of alert Rhesus monkeys under different conditions of visual-vestibular stimulation. Stimulations conditions were vestibular, optokinetic, combined and conflicting. About 10--20% of all P-cells were activated in their simple spike activity during conflicting stimulation to the recording side (type I) and gave no response or much less during vestibular stimulation. About half of these P-cells were also activated during optokinetic stimulation to the recording side at velocities above 40--60 deg/s. Simple and complex spike activity behaved in a reciprocal way with overlapping but not identical working ranges. Simple spike modulation was unidirectional, complex spike activity always bidirectional. Modulation of simple spike activity cannot be related to one single parameter of the sensory input or the oculomotor output. The hypothesis is put forward that the vestibular nuclei and the flocculus behave in a complementary fashion in processing visual-vestibular information, the flocculus being specialized for high velocity optokinetic nystagmus and suppression of vestibular nystagmus.

Journal ArticleDOI
TL;DR: The anatomical results show that there is ample opportunity for electrosensory information arising on left and right sides of the body to interact centrally, and one can suggest that comparison of afferent input from the two sides would reduce the non-significant variability which affects both of them equally.
Abstract: Primary electroreceptor afferents terminate in the posterior lateral line lobe (PLLL) in electroreceptive teleosts. This paper examines the central connections of PLLL in fish of the family Mormyridae using horseradish peroxidase and tritiated amino acid tracing techniques. Some connections of the closely related lobus caudalis of the cerebellum are also examined. There are three zones on each side of the mormyrid PLLL cortex. Two receive input from mormyromast receptors, and one from ampullary receptors. An intrazonal projection system, intrinsic to PLLL, connects neighboring points within each zone. It also joins corresponding zones on the two sides of the body via commissural fibers. An interzonal system connects the two mormyromast zones on the same side of the midline. Central structures which project to PLLL include lobus caudalis, nucleus paratrigeminalis lateralis, and nucleus praeeminentialis. Nucleus praeeminentialis projects bilaterally and somatotopically to the lower molecular layer of PLLL. PLLL cortex projects bilaterally and somatotopically to two major mesencephalic sites: n. praeeminentialis, and n. lateralis. Somatotopically corresponding points in each zone of PLLL cortex project to the same small region of n. lateralis. Nucleus lateralis has a large and somatotopically organized projection to n. praeeminentialis. The afferent and efferent connections of lobus caudalis are similar to those of PLLL, indicating its close association with the electrosensory system. The anatomical results show that there is ample opportunity for electrosensory information arising on left and right sides of the body to interact centrally. One can suggest that comparison of afferent input from the two sides would reduce the non-significant variability which affects both of them equally. The results also show the presence of several somatotopically organized feedback lops which return the results of higher order processing of electrosensory information to earlier stages.

Journal ArticleDOI
TL;DR: The results show that the prelunate cortex has access to an extraretinal signal which is activated in association with events preceding visually guided eye movements, which reflects the initiation of eye movement or the animal's interest in the stimulus.
Abstract: Single unit recording from trained rhesus monkeys demonstrate that the activity of the prelunate cortex is enhanced when a visual stimulus becomes a target of saccadic eye movement. As a rule, the enhancement is spatially selective: it does not occur if the animal makes an eye movement away from, rather than towards the stimulus. The results show that the prelunate cortex has access to an extraretinal signal which is activated in association with events preceding visually guided eye movements. Whether the signal reflects the initiation of eye movement or the animal's interest in the stimulus, which he usually selects to initiate an eye movement, remains uncertain.

Journal ArticleDOI
TL;DR: Part of the flocculus — as further discussed elsewhere — may be specialized to subserve visual-vestibular interaction to improve the nystagmus response.
Abstract: Neuronal activity in the flocculus of alert Rhesus monkeys was recorded during vestibular stimulation (rotation of the monkey about a vertical axis in complete darkness), optokinetic stimulation (rotation of the visual surround around the stationary monkey), combined visual-vestibular stimulation (rotation of the monkey inside the stationary surround in the light), and conflicting visual-vestibular stimulation (rotation of the monkey together with the visual surround in the same direction). The input to the flocculus was recorded as non-Purkinje cell (non-P-cell) activity. Ninety per cent of the non-P-cells which were modulated during our stimulation paradigms carry information similar to that in the neurons of vestibular nuclei. This suggests that the main mossy fiber input to the flocculus originates in the vestibular nuclei. A second input of unknown origin conveys visual information about retinal slip. Thus, part of the flocculus — as further discussed elsewhere (Waespe and Henn 1981) — may be specialized to subserve visual-vestibular interaction to improve the nystagmus response.

Journal ArticleDOI
TL;DR: These stereospecific actions of baclofen, produced by either a reduction in the release of excitatory transmitter or postsynaptic antagonism, suggest that Ia, Ib, and Aα afferents may release the same excitational transmitter which differs from that of spinal excitatories interneurones.
Abstract: When ejected microelectrophoretically near spinal interneurones of cats anaesthetised with pentobarbitone and under conditions where postsynaptic excitability was maintained artificially at a constant level, (−), but not (+), -baclofen selectively reduced monosynaptic excitation by impulses in low threshold muscle (Ia and Ib) and cutaneous (Aα) afferents. Polysynaptic excitation of interneurones and Renshaw cells by impulses in higher threshold afferents was less affected, and baclofen had little or no effect on the cholinergic monosynaptic excitation of Renshaw cells. Glycinergic and gabergic inhibitions of spinal neurones were relatively insensitive to baclofen. These stereospecific actions of baclofen, produced by either a reduction in the release of excitatory transmitter or postsynaptic antagonism, suggest that Ia, Ib, and Aα afferents may release the same excitatory transmitter which differs from that of spinal excitatory interneurones.

Journal ArticleDOI
TL;DR: In this paper, single and double retrograde tracer techniques were employed in cats to investigate the topographical relationships between supraspinal neurons projecting to either the brachial or lumbosacral enlargement.
Abstract: Single and double retrograde tracer techniques were employed in cats to investigate: (1) the topographical relationships between supraspinal neurons projecting to either the brachial or lumbosacral enlargement, (2) the distribution and relative frequency of single supraspinal neurons which project to both enlargements by means of axonal branching. In one group of cats large injections of horseradish peroxidase (HRP) were made throughout either the brachial or lumbosacral enlargement. The results from these experiments support recent observations on the multiplicity of brainstem centers giving origin to descending spinal pathways and provide evidence for a population of corticospinal neurons in area 6. In a second set of experiments, HRP was injected in one enlargement, and 3H-apo-HRP (enzymatically inactive) was injected in the other enlargement. Relatively large numbers of neurons with collateral projections to both enlargements (double-labeled) were observed in the medullary and pontine reticular formation, the medial and inferior vestibular nuclei bilaterally, the ipsilateral lateral vestibular nucleus, Edinger-Westphal nucleus, caudal midline raphe nuclei and nuclear regions surrounding the brachium conjunctivum. By contrast, double-labeled neurons were infrequently observed in the red nucleus and sensorimotor cortex, contralateral to the injections. In the red nucleus, lateral vestibular nucleus and sensorimotor cortex, neurons projecting to the brachial enlargement were largely segregated topographically from neurons projecting to the lumbosacral enlargement. However, there was some overlap, and double-labeled neurons were consistently observed within the region of overlap. In the sensorimotor cortex, the overlap between brachial- and lumbar-projecting neurons was most prominent in areas 4 and 3a, along the cruciate sulcus, but also involved other cytoarchitectonic regions in the medial aspect of the hemisphere.

Journal ArticleDOI
TL;DR: Fourteen chicks were hatched and reared in darkness to approximately equal to 21 h when they were exposed to overhead illumination for 0.5 h and then to an imprinting stimulus (a pulsing red light) for 20 min and matched in pairs on the basis of their activity.
Abstract: Fourteen chicks were hatched and reared in darkness to approximately equal to 21 h when they were exposed to overhead illumination for 0.5 h and then to an imprinting stimulus (a pulsing red light) for 20 min. The chicks were then matched in pairs on the basis of their activity. One member of each pair was returned to the dark and the other was trained for a further 120 min. All chicks were killed approximately equal to 6.5 h after the onset of training and perfused with fixative. Blocks were removed bilaterally from a restricted part of the hyperstriatum ventrale and prepared for electron-microscopy. Various synaptic features were measured, all counts being performed 'blind'. In undertrained chicks the length of the synaptic apposition zone in this part of the left hemisphere was shorter than that in the right by a mean value of 35 +/- 11.4 (SEM) nm. Further training eliminated this difference. No other synaptic measurements were affected by prolonging the period of training.

Journal ArticleDOI
TL;DR: It is suggested that during the stance phase of heel bipedal locomotion, the cutaneous depression of Ib reflex pathways to MNs supplying muscles operating at the knee might operate in association with the strong Ia connexions from ankle to knee muscles described in the previous paper.
Abstract: Variations in the H-reflex of soleus (Sol), quadriceps (Q) and short head of biceps femoris (Bi) muscles in normal man were used to investigate the effect of volleys in low threshold cutaneous afferents from the ipsilateral limb on transmission of Ib effects from ankle and Q muscles to these different motoneurone (MN) pools. Stimulation of cutaneous afferents from the foot sole and the toes (but not from the thigh, knee or calf), which did not modify the size of the test reflexes when applied alone, strongly depressed Ib reflex pathways to MNs supplying muscles operating at the knee. The very brief central latency of this depression suggests that tactile cutaneous afferents from the foot have oligosynaptic spinal connexions with the interneurones intercalated in the Ib pathways to MNs. The same cutaneous stimuli did not at all modify Ib inhibition of Sol MNs from triceps surae. These findings are discussed with regard to the role of the different muscles in human locomotion. It is suggested that during the stance phase of heel bipedal locomotion, the cutaneous depression of Ib reflex pathways to MNs supplying muscles operating at the knee might operate in association with the strong Ia connexions from ankle to knee muscles described in the previous paper.

Journal ArticleDOI
TL;DR: It is concluded that the C3-C4 PNs projecting to forelimb motoneurones can be excited not only from the cortico-, rubro-, and tectospinal tracts but also by reticulospinal fibres.
Abstract: Effects of stimulation in the medullary reticular formation (RF) on C3-C4 propriospinal neurones (PNs) were investigated in two series of experiments: (1) indirectly by analyzing how propriospinal transmission to forelimb motoneurones is modified by reticular stimuli; (2) directly by intracellular recording from C3-C4 neurones, which were identified as propriospinal by their antidromic activation from the C6 segment. Propriospinally mediated disynaptic EPSPs evoked in motoneurones from the pyramid (Pyr) and the red nucleus (NR) were effectively facilitated by conditioning stimulation in the RF with a time course of facilitation indicating monosynaptic linkage to the PNs. Propriospinally mediated trisynaptic IPSPs were facilitated less regularly and sometimes instead depressed by conditioning stimulation in the RF. The depression is at least partly due to inhibition of the first order PNs. Recording from C3-C4 PNs revealed that many of them were excited or inhibited by single stimuli in the RF. The brief latency of the EPSPs evoked in these neurones shows monosynaptic linkage from fast reticulospinal fibres. Some IPSPs were similarly monosynaptically evoked from fast fibres and observations are presented suggesting that longer latency IPSPs are monosynaptically mediated by slower fibres. Facilitation of propriospinal transmission to motoneurones as well as the EPSPs and IPSPs in PNs were evoked from a region within or close to the nucleus reticularis gigantocellularis. Convergence of monosynaptic EPSPs from Pyr, NR, tectum, and RF was common in C3-C4 PNs. Linear summation of the EPSPs from RF with those evoked from cortico-, rubro-, or tectospinal tracts shows that the former are not due to stimulation of collaterals which the latter tracts may have in RF. Mediation of the EPSPs and IPSPs by descending, rather than by antidromically activated ascending fibres, was indicated by temporal facilitation produced by RF stimuli, subliminal for evoking monosynaptic PSPs in the PNs. Stimulation of the labyrinth did not evoke disynaptic PSPs in any of the PNs investigated. It is concluded that the C3-C4 PNs projecting to forelimb motoneurones can be excited not only from the cortico-, rubro-, and tectospinal tracts (Illert et at. 1977, 1978) but also by reticulospinal fibres.

Journal ArticleDOI
TL;DR: It is suggested that the central nervous system may monitor muscle afferent activity of the lengthening (antagonist) muscle during simple, step movements.
Abstract: Muscle tendon vibration was applied during voluntary step-tracking arm target-movements performed by normal human subjects. Vibration (freq. = 120 Hz) was applied over either the biceps or triceps tendons. During non-visually guided (eyes closed) trials, vibration of the muscle antagonistic to the movement being performed resulted in an undershoot of the required target. Thus, biceps vibration produced an undershoot of the extension target and triceps vibration an undershoot of the flexion target. The same effect occurred if the vibration was applied continuously over several movements or only during the course of individual movements. In contrast, vibration of the muscle acting as the prime mover had no effect on the correct attainment of the required target. It is suggested that the central nervous system may monitor muscle afferent activity of the lengthening (antagonist) muscle during simple, step movements.

Journal ArticleDOI
TL;DR: Early visual deprivation alters the associative systems of the brain by reducing the efficiency of transmission along pathways that mediate visual influences, which may explain the lasting behavioural alterations that take place in man and monkeys after prolonged visual deprivation at an early age.
Abstract: Clinical experience from humans deprived of vision at an early age indicates that recovery of vision is often rudimentary after late correction of the abnormalities in the eyes. Binocular deprivation in cats does not change the function of the visual cortex equally much as does monocular deprivation. Therefore, the behavioural blindness observed after binocular deprivation is probably caused by changes central to area 17. We studied four monkeys deprived of vision by binocular lid closure from shortly after birth until the ages of 7 to 11 months and three control animals of the same age. After opening, the eyes of the deprived animals were normal, optokinetic nystagmus could be elicited, and microelectrode recordings of multiple unit activity in areas 17 and 19 indicated brisk responses to visual stimulation. Behaviourally, all deprived animals were blind, however. They bumped into obstacles, fell from tables and used their somatic sense for exploration. Only minute recovery of visual orientation was observed during several months after the opening of the eyes. Approximately 400 multiple unit recording penetrations were made in Brodmann's area 7 in the deprived monkeys and a similar number in the control monkeys using the transdural recording technique in conscious, behaving animals. The results indicated a profound decrease in the representation of vision in this area: the representation of visual mechanisms was reduced by 92% and the combined visual and somatic representation was reduced by 97% in the deprived monkeys. On the other hand, the representation of active somatic movement had increased by 117% and that of passive somaesthesia by 53%. Also the proportion of cell groups that could not be activated (only spontaneously active) increased fourfold. These results show that early visual deprivation alters the associative systems of the brain by reducing the efficiency of transmission along pathways that mediate visual influences. Inputs from different sensory systems may compete for influence on the association cortex, disuse in one leading to its functional deterioration. Such changes may explain the lasting behavioural alterations that take place in man and monkeys after prolonged visual deprivation at an early age.

Journal ArticleDOI
TL;DR: It is found that significant sparing or recovery of hindlimb locomotor function is closely linked to sparing of axons in at least one ventrolateral quadrant of the cord.
Abstract: We trained cats to walk on a moving treadmill belt, then subjected them to partial transverse sections of the thoracic spinal cord Afterwards, we observed their ability to walk on the treadmill, over a period of several weeks, using gait analysis techniques to describe the resultant deficits The extent of the lesions was verified histologically, and the identity of the spared descending axons from the brain stem was demonstrated by retrograde labeling with horseradish peroxidase We found that significant sparing or recovery of hindlimb locomotor function is closely linked to sparing of axons in at least one ventrolateral quadrant of the cord The essential elements probably belong to vestibulospinal and reticulospinal systems

Journal ArticleDOI
TL;DR: The small size of the area where strong flank suppression occurred shows that inhibition comes from a few LGN cells rather than from a large pool of cells, consistent with the interpretation that simple cells have excitatory and inhibitory input from the same type of cells in the lateral geniculate nucleus (LGN), i.e., only from ON-center or OFF-center cells.
Abstract: The receptive field organization of simple cells was studied by analyzing interaction effects between two stationary flashing light stimuli. One stimulus was positioned in the most responsive part of the receptive field to produce activity against which the effects of the other stimulus in various positions of the visual field could be determined.

Journal ArticleDOI
TL;DR: In many nBOR units, the preferred and null directions are not opposite to each other, and these directional asymmetries seem to be correlated with other properties of the units in a manner that supports the idea that the accessory optic system is arranged according to a vestibular coordinate system.
Abstract: Single unit recordings in the nucleus of the basal optic root (nBOR) of the accessory optic system in chickens suggest that it has a role in vertical stabilizing eye movements. Cells have unusually large receptive fields and never respond to small stationary stimuli. They respond best to large richly patterned stimuli moving slowly (2–4 °/s) in vertical directions. Cells responsive to upward movement tend to be located in the dorsal portion of nBOR, which projects to motor areas producing upward eye movement, whereas cells responsive to downward movement tend to be located in the ventral portion of nBOR, which projects to motor areas producing downward eye movement; this suggests that these synapses onto oculomotor neurons are excitatory.

Journal ArticleDOI
Josef Zihl1
TL;DR: In this paper, it is suggested that recovery takes place at the level of the striate cortex and is probably mediated by the retino-tectal pathway, and the degree of recovery was related to the sharpness of the visual field border, whereas in patients with a rather shallow gradient of light sensitivity in the area between the intact visual field and the scotoma, a fairly good recovery was obtained.
Abstract: Patients with homonymous visual field defects after damage to the geniculo-striate pathway were forced to make saccadic eye movements to light targets presented briefly in their perimetrically blind regions. This specific type of saccadic localization led to an increase in visual field size in the region subjected to this practice. Visual acuity and color identification also improved in the restored region, provided that the lesion was mainly limited to the striate cortex. The enlargement of the visual field strongly depended on a specific practice. The degree of recovery was related to the sharpness of the visual field border. In patients with a rather shallow gradient of light sensitivity in the area between the intact visual field and the scotoma, a fairly good recovery was obtained, whereas in patients with a steeper gradient the enlargement of the visual field was small. It is suggested that recovery takes place at the level of the striate cortex and is probably mediated by the retino-tectal pathway.