Showing papers in "Experimental Brain Research in 1982"

Visual Neurones Responsive to Faces in the Monkey Temporal Cortex

Abstract: Of 497 single neurones recorded in the cortex in the fundus of the superior temporal sulcus (STS) of three alert rhesus monkeys, a population of at least 48 cells which were selectively responsive to faces had the following response properties: (1) The cells' responses to faces (real or projected, human or rhesus monkey) were two to ten times as large as those to gratings, simple geometrical stimuli or complex 3-D objects. (2) Neuronal responses to faces were excitatory, sustained and were time-locked to the stimulus presentation with a latency of between 80 and 160 ms. (3) The cells were unresponsive to auditory or tactile stimuli and to the sight of arousing or aversive stimuli. (4) The magnitude of the responses of 28 cells tested was relatively constant despite transformations, such as rotation, so that the face was inverted or horizontal, and alterations of colour, size or distance. (5) Rotation to profile substantially reduced the responses of 21 cells (31 tested). (6) Masking out or presenting parts of the face (i.e. eyes, mouth or hair) in isolation revealed that different cells responded to different features or subsets of features. (7) For several cells, responses to the normal organisation of cut-out or line-drawn facial features were significantly larger than to jumbled controls. These findings indicate that explanations in terms of arousal, emotional or motor reactions, simple visual feature sensitivity or receptive fields are insufficient to account for the selective responses to faces and face features observed in this population of STS neurones. It appears that these neurones are part of a system specialised to code for faces or features present in faces, and it is suggested that damage to this system is related to prosopagnosia, or difficulty in face recognition, in man and to the tameness and social disturbances which follow temporal lobe damage and are part of the Kluver-Bucy syndrome in the monkey.

Kinaesthetic role of muscle afferents in man, studied by tendon vibration and microneurography

Abstract: The characteristics of vibration-induced illusory joint movements were studied in healthy human subjects. Unseen by the subject, constant frequency vibration trains applied to the distal tendon of the Triceps or Biceps induced an almost constant velocity illusory movement of the elbow whose direction corresponded to that of a joint rotation stretching the vibrated muscle. Vibration trains of the same duration and frequency applied alternatively to the Biceps and Triceps evoked alternating flexion-extension illusory movements. During successive application of vibration trains at frequencies from 10 to 120 Hz, the perceived velocity of the illustory movements increased progressively from 10 to 70-80 Hz, then decreased from 80 to 120 Hz. The maximal perceived velocity was three times higher during alternating vibration of the Biceps and Triceps than during single muscle stimulation. Unit activity from 15 muscle spindle primary endings and five secondary endings located in Tibialis anterior and Extensor digitorum longus muscles were recorded using microneurography in order to study their responses to tendon vibration and passive and active movements of the ankle. Primary endings were all activated by low amplitude tendon vibration (0.2-0.5 mm) previously used to induce illusory movements of the elbow. The discharge of some was phase-locked with the vibration cycle up to 120 Hz, while others responded one-to-one to the vibration cycle up to 30-50 Hz, then fired in a sub-harmonic manner at higher frequencies. Secondary endings were much less sensitive to low amplitude tendon vibration. Primary and secondary ending responses to ramp and sinusoidal movements of the ankle joint were compared. During the movement, the primary ending discharge frequency was almost constant, while the secondary ending activity progressively increased. During ankle movements the primary ending discharge appeared mainly related to velocity, while some secondary activities seemed related to both movement velocity and joint angle position. Muscle spindle sensory ending responses to active and passive ankle movements stretching the receptor-bearing muscle (plantar flexion) were qualitatively and quantitatively similar. During passive reverse movements (dorsiflexion) most of the sensory endings stopped firing when their muscle shortened. Active muscle shortening (isotonic contraction) modulated differently the muscle spindle sensory ending discharge, which could stop completely, decrease or some times increase during active ankle dorsiflexion. During isometric contraction most of the muscle spindle sensory endings were activated. The characteristics of the vibration-induced illusory movements and the muscle spindle responses to tendon vibration and to active and passive joint movements strengthened the possibility of the contribution of primary endings to kinesthesia, as suggested by several previous works...

Orientation selectivity in the cat's striate cortex is invariant with stimulus contrast

Abstract: Extracellular responses of single units in striate cortex of the cat were studied quantitatively. Sinusoidal gratings were used as stimuli and the variables of interest were orientation and contrast. Specifically, we wanted to determine if orientation tuning was dependent on contrast. Of 45 cells studied in detail, two basic types of contrast-response pattern were observed, but most patterns were intermediate between these extremes. In one type, responses increased approximately linearly with log contrast while in the second, saturation was found at low contrast levels. For all these cells, orientation tuning characteristics were independent of contrast. An additional observation, made from 14 cells, was that stimuli presented at non-optimal orientations can suppress responses to below the general maintained discharge levels. In eight of these cases, the inhibition was clearly contrast-dependent.

The coordination of eye, head, and arm movements during reaching at a single visual target

Abstract: The time of occurrence of eye, head, and arm movements directed at the same visual target was measured in five human subjects. The latency of activation of the corresponding neck and arm muscles was also measured. It appears that although the overt movements are sequentially ordered (starting with the eye movement, then the head and finally the arm) the EMG discharges are synchronous with respect to the eye movement onset. In addition, eye movement latency appears definitely (though weakly) correlated with either neck or arm EMG latencies. Neck and arm EMG latencies are also mutually correlated. These results indicate a clustering of segmental motor programs for target oriented actions.

Arm trajectory formation in monkeys.

Abstract: The formation of forearm trajectories of moderate velocities (0.3–1.3 rad/s) was studied in monkeys performing a simple visuomotor task. The experiments were designed to test the hypothesis that the transition from one position to another is subserved by a rapid shift to a final equilibrium of forces in agonist and antagonist muscles. This idea is attractive because it suggests the possibility that in simple movements the trajectory is determined by the inherent inertial and viscoelastic properties of the limb and muscles around a joint. The results indicate that these moderate speed movements are controlled by a gradual, and not a step-like, shift to the final equilibrium position.

An Autoradiographic Study of Efferent Connections of the Globus Pallidus in Macaca mulatta

Abstract: Radioactive amino acids were injected into restricted regions of the globus pallidus of rhesus macaques to allow identification of the organization and courses of efferent pallidal projections. The previously identified projection of the internal pallidal segment (GPi) to ventral thalamic nuclei showed a topographic organization, with the predominant projection from ventral GPi being to medial and caudal ventralis anterior (VA) and lateralis (VL) and from dorsal GPi to lateral and rostral VA and VL. Pallidal efferent fibers also extended caudally and dorsally into pars caudalis of VL, but they spared the portion of pars oralis of VL shown by others to receive input from the cerebellum. In addition to centromedian labeling in all animals, the parafascicular nucleus was also labeled when isotope was injected into dorsal GPi. The medial route from GPi to the midbrain tegmentum was more substantial than has been shown before, and along this route there was an indication that some fibers terminated in the prerubral region. The projection to the pedunculopontine nucleus was extensive, and fibers continued caudally into the parabrachial nuclei. Pallidal projections to the thalamus seem to be topographically organized but spare thalamic regions that interact with area 4. Caudally directed efferent fibers follow multiple routes and extend more caudally than to the pedunculopontine nuclei.

Characterization of L-glutamate uptake into and release from astrocytes and neurons cultured from different brain regions.

Abstract: The uptake of L-glutamate was studied in astrocytes cultured from different brain areas of newborn rats as well as in two different cultures of neurons obtained from mouse brain. Both astrocytes and neurons exhibited high-affinity glutamate uptake with Km values ranging from 34 [μM to 82 μM. Vmax values for astrocytes cultured from the different brain regions were: prefrontal cortex: 13.9; occipital cortex: 11.4; neostriatum: 27.3 and cerebellum: 5.8 nmol · min−1 · mg−1 cell protein. For cerebellar granule cells and cerebral cortical neurons the Vmax values were found to be 10.2 and 5.9 nmol · min−1 · mg−1 cell protein, respectively. The effect on L-glutamate uptake in astrocytes cultured from prefrontal cortex and in cultured cerebellar granule cells of a series of compounds structurally related to glutamate was studied, and detailed kinetic analyses of the inhibitory patterns of three potent inhibitors were performed. L-aspartate and L-aspartate-β-hydroxamate were found to be competitive inhibitors of L-glutamate uptake in both cell types with Ki values for astrocytes of 60 μM and 91 [μM, respectively, and for granule cells of 48 μM and 72 μM, respectively. D-aspartate was found to be a mixed-type noncompetitive inhibitor of L-glutamate uptake in astrocytes (K;: 106 μM), but in granule cells this compound showed simple competitive inhibition with a Ki of 49 μM. Sodium dependency of L-glutamate uptake in both cell types was studied at a series of Lglutamate and Na+ concentrations. It was found that the uptake of glutamate in astrocytes is coupled with one Na+ ion in contrast to two Na+ ions in granule cells. The Km value for sodium was found to be 15 mM in both cell types. It was shown that release of exogenously supplied [3H] -L-glutamate from cerebel lar granule cells could be stimulated in a Ca2+-dependent manner by high concentrations (55 mM) of K+. In contrast to this no K+-induced release of glutamate could be demonstrated in cultured astrocytes.

Axonal patterns and sites of termination of cat superior colliculus neurons projecting in the tecto-bulbo-spinal tract

Abstract: Horseradish peroxidase was injected in the somata or axons of neurons located in the intermediate and deep layers of the superior colliculus. A group of 34 neurons with physiologically identified projection in the predorsal bundle (tectobulbo-spinal neurons, TBSNs) and two commissural tecto-tectal neurons were characterized with regard to soma-dendritic profiles, axon trajectories, collateral branching, and terminations.

Changes in the total number of dentate granule cells in juvenile and adult rats: A correlated volumetric and 3H-thymidine autoradiographic study

Abstract: The total number of granule cells in the dentate gyrus was estimated in 17 male rats, four each aged 30, 120, and 200 days, and five aged 365 days. There is a substantial 35–43% linear increase between 1 month and 1 year. Two parameters of the granular layer are involved in the numerical change. First, total granular layer volume grows linearly with age. Second, average volume of a single granule cell nucleus in the ventral dentate gyrus decreases with age. Older rats tend to have a larger granular layer filled with more and smaller cells. In another group of 21 male rats, 3H-thymidine injections were given on four consecutive days during juvenile (30–33, n = 6) and adult life (60–63, n = 5; 120–123, n = 6; 180–183, n = 4). All animals survived to 200 days of age. The proportion of labeled mature granule cells and labeled presumptive granule cell precursors were determined in anatomically-matched slices. With older ages at injection, there is a decline in labeled mature granule cells and a concurrent increase in labeled precursors. These data are compatible with the constant level of granule cell increase determined volumetrically. Most of the late granule cells originate nearly simultaneously along the base of the main bulk of the granular layer; very few are found in the dorsal tip (septal extreme) and ventral tip (temporal extreme). This study is the first demonstration of a net numerical gain in a neuronal population during adulthood in the mammalian brain. Since the granule cells play a pivotal role in hippocampal function, these data suggest that their influence grows with age.

Temporal properties of the visual detectability of moving spatial white noise.

Abstract: We obtained movement detection thresholds for two-dimensional random speck-patterns ("Julesz" patterns) homogeneously moving over the whole target field (5.21 x 5.31 degrees of visual angle). We alternated between two uncorrelated but otherwise similar patterns, one moving with velocity leads to V1, the other with velocity leads to V2, such that each pattern was on for T ms. We masked this pattern (signal) with spatio-temporal white noise ("snow"). The total r.m.s. contrast was kept constant, whereas the ration of the r.m.s. contrasts of signal and noise was varied. The square of this ratio was designated SNR. At low SNR values the pattern was not perceptually different from the snow alone. At high SNR values the subject detected spatio-temporal correlation (e.g., movement). In these experiments we determined the threshold SNR values as a measure of the detectability of spatio-temporal correlation as a function of the parameters T, leads to V1, and leads to V2. When leads to V1 and leads to V2 were sufficiently dissimilar one of three percepts occurred: for very large T the alternation could be followed, for very small T two transparent, simultaneously moving sheets of noise-pattern with different velocities could be seen. For intermediate T-values no systematic movement at all could be observed. At these T-values the threshold SNR was maximal. This "'critical" T-value decreased with increasing velocity. We found that it was possible to have more than one percept of uniform smooth movement at a single location in the visual field if these movements had velocity vectors with an angular difference of at least 30 deg or if their magnitudes differed by at least a factor of 4.

Physiologic and anatomic investigation of a visual cortical area situated in the ventral bank of the anterior ectosylvian sulcus of the cat

Abstract: In this paper a cortical area is described that covers approximately the posterior two-thirds of the ventral bank of the anterior ectosylvian sulcus of the cat and is called anterior ectosylvian visual area (AEV).

Stimulus-induced changes in extracellular Na+ and Cl- concentration in relation to changes in the size of the extracellular space

Abstract: Extracellular Na+- and Cl−-concentrations ([Na+]o, [Cl−]o) were recorded with ion-selective microelectrodes during repetitive stimulation and stimulus-induced self-sustained neuronal afterdischarges (SAD) in the sensorimotor cortex of cats. In all cortical layers [Na+]o initially decreased by 4–7 mM. In depths of more than 600 μm below the cortical surface such decreases usually turned into increases of 2–6 mM during the course of the SADs, whereas in superficial layers [Na+]o never rose above its resting level. [Cl−]o always showed an increase in the course of the SADs often preceded by an initial small decrease. The average increase at a depth of 1,000 μm was about 7 mM. [Cl−]o reached peak values at about the end of the ictal period, whereas [Na+]o reached its maximum shortly after the end of the SAD, at times when [K+]o was still elevated above the baseline concentration.

Orientation sensitivity of cat LGN neurones with and without inputs from visual cortical areas 17 and 18

Abstract: Orientation sensitivity was tested, using moving bars as stimuli, in 136 LGN cells in normal cats and 82 LGN cells in cats with areas 17 and 18 lesioned. The responses of most neurones showed some dependence on the orientation of the line stimulus. The orientation bias was more pronounced for long, narrow bars moving at rather slow velocities. Length-response curves revealed less end-inhibition along the optimum orientation than along the non-optimum orientation. Thiry-two percent of the cells in the normal cats and 50% in the lesioned animals responded best to orientations within 10 degrees of the vertical or horizontal. The oblique orientations were represented poorly in the lesioned group. Thus the corticogeniculate feedback may serve to confer a more uniform distribution of orientation preferences on the LGN. It is suggested that the orientation biases of LGN neurones may play a role in building orientation-selective cells in the visual cortex. Further, the preferences for horizontal and vertical orientations in the LGN may explain the preferences for these orientations reported for visual cortical cells.

Time course and properties of late adaptation in spinal motoneurones of the cat.

Abstract: In the spinal cord of anaesthetized cats, motoneurones of m.gastrocnemius medialis were stimulated to repetitive firing by very long-lasting steady currents injected through an intracellular microelectrode (maximum duration 4 min). In such discharges, a gradual decline of impulse frequency was found to occur during several tens of seconds. Most of this “late adaptation” occurred during the first 30 s of firing. Comparisons between the responses of different cells showed that the frequency-drop during late adaptation was strongly correlated to the impulse rate at the beginning of the discharge. For one and the same cell, late adaptation was more prominent at strong than at weaker intensities of stimulation (i.e., at high than at lower initial firing rates). In cells capable of discharging continuously for several minutes, a semi-stationary discharge rate tended to be reached after about 1 min or less.

Specific effects of unilateral lesions in the flocculus upon eye movements in albino rabbits.

Abstract: The horizontal vestibulo-ocular reflex (HVOR) and optokinetic response (OKR) were examined in alert albino rabbits following unilateral flocculectomy. Chemical flocculectomy with local application of kainic acid was used to avoid the retrograde degeneration of inferior olive neurons that accompanies surgical flocculectomy. Effects of chemical flocculectomy, however, were identical to those of surgical flocculectomy. The following functional deficiencies were observed in the movements of the ipsilateral eye: (1) reduction of the HVOR gain; (2) increased lag of the HVOR phase; (3) increased non-linearity of the relationship between the HVOR gain and the amplitude of turntable rotation; (4) decreased OKR gain; (5) delay with increased variation in the OKR phase; (6) impairment of rapid visual-vestibular interaction; (7) loss of the adaptation of the HVOR. Only a transient depression of the HVOR gain was seen in the contralateral eye. Control experiments with lesions in the paraflocculus, nodulus, and uvula, or lobules VI and VII, revealed no such deficiencies, except that lesions in the nodulus and uvula produced marked advancement of the HVOR phase. The effects of flocculectomy are consistent with present knowledge of both neuronal circuitry and activity of the rabbit flocculus.

Firing rates and patterns of midbrain reticular neurons during steady and transitional states of the sleep-waking cycle

Abstract: Spontaneous firing of midbrain reticular formation (MRF) neurons was recorded extracellularly in chronically implanted, behaving cats during steady and transitional states of the sleep-waking cycle. Physiological identification of receiver and/or projection MRF neurons was achieved through orthodromically and antidromically elicited discharges.

Microstimulation of the supplementary motor area (SMA) in the awake monkey

Abstract: The supplementary motor area of threeMacaca fascicularis was mapped using intracortical microstimulation (ICMS). Both forelimb and hindlimb movements were evoked using currents of 30 μA or less. However, thresholds for evoking movements were higher than those in the primary motor cortex. Proximal motor effects predominated, but distal joint movements were also elicited. Forelimb points were clustered in mesial cortex of area 6, anterior to the precentral hindlimb and tail region. Distal joint effects were located deep in the cortex, intermingled with proximal effects. Hindlimb responses which were less spatially localized, were found both ventral to the forelimb area, in the dorsal bank of the cingulate sulcus, and in mesial cortex, well anterior to area 4. No movements of facial muscles were elicited. Injections of HRP were made into the spinal cord at the cervical level in two animals and the lumbar level in the third one. An area of labelled cells was seen in mesial area 6 which corresponded closely to the region from which ICMS effects were elicited. No movements were evoked from the anterior portions of the fundal region of the cingulate sulcus which were also labelled.

Long latency reflexes to imposed displacements of the human wrist: dependence on duration of movement.

Abstract: Reflex EMG responses to angular displacements of the wrist joint were recorded from 12 normal human volunteers. A mechanical stop was used to suddenly arrest displacements at varying times following the onset of the stimulus. With unrestricted movement of the handle, the EMG response consisted of an early component (M1) with a latency of 30–35 ms and a long-latency component (M2–3) beginning 55–65 ms after the onset of the displacement. When the displacements were arrested prior to a critical time occurring between 40 and 50 ms after the onset (mean of 44 ms), the M2–3 component of the response was not present. Increasing the duration of the displacement beyond this time resulted in a rapid increase in the size of M2–3. Facilitation provided by volitional intent to oppose the perturbation was not sufficient to generate an M2–3 response to either a brief, low velocity displacement produced by the torque motor or to a phasic, high velocity stretch produced by a tendon tap.

A note on the transneuronal transport of wheat germ agglutinin-conjugated horseradish peroxidase in the avian and rodent visual systems.

Abstract: While using horseradish peroxidase conjugated to the plant lectin wheat germ agglutinin (WGA-HRP) as an anterograde marker to label the developing retinofugal projection in the chick, we have found that a significant amount of the tracer can escape from the axons and axon terminals of retinal ganglion cells and be subsequently taken up and transported both anterogradely and retrogradely by neighboring neurons and/or axon terminals. The release and uptake of the tracer appears to be nonspecific, and is particularly striking at embryonic stages; at these stages there is also appreciable uptake of the WGA-HRP by ependymal cells and by radial glial processes. Subsequent experiments in rats have shown that as early as 2 days after an injection of WGA-HRP into an eye there is clear labeling of geniculo-cortical axons in the striate cortex. Since WGA-HRP is being used increasingly in neuroanatomical studies, it is now clear that when interpreting the results of experiments with this marker the possibility of transneuronal labeling must be borne in mind, and especially after relatively long post-labeling survival periods. At the same time the secondary transport of WGA-HRP may, in certain neural systems, provide a useful tool for analyzing second-order connections.

Motoneurone properties and motor fatigue

Abstract: Gastrocnemius motoneurones with different types of muscle unit were compared with respect to their repetitive discharges during 4 min periods of steady intracellular stimulation. The cells were activated by a constant injected current of 5 nA above threshold. Among neurones capable of discharging for 10 s or more, the discharge duration showed no significant correlation to the contraction time or amplitude of the muscle unit twitch. Neither was there any obvious correlation between discharge duration and the sensitivity to contractile fatigue. The slow drop in discharge rate, as measured from the 2nd to the 26th s of firing, was more pronounced for fast-twitch units than for the ones with a slower twitch. Among fast-twitch neurones with about the same initial discharge rate, no difference in the extent of slow frequency drop was found between cells with fatigue-resistant and fatigue-sensitive muscle units. For fast-twitch neurones, measurements and calculations showed that, if the effects of peripheral potentiation and fatigue were disregarded, the drop in firing rate was great enough to cause a decrease in force by more than 60% during the first minute of constant stimulation. Among the fast-twitch units studied, the mean recorded fall in contractile force was initially less than expected (potentiation dominating) and it had become about equal to the expected one at 1 min after the onset of the discharge. It is concluded that, particularly with respect to fast-twitch motoneurones, the late adaptation is likely to be a significant factor for the development of central “fatigue” in voluntary or reflex contractions. Thanks to their small amount of late adaptation, slow-twitch motoneurones are par ticularly suitable for producing a steady postural contraction.

Horizontal Eye Position-related Activity in Neck Muscles of the Alert Cat

Abstract: The activity of neck muscles was recorded in the alert, head-fixed cat together with the horizontal and vertical components of eye movements. Electromyographic activity of obliquus capitis cranialis and caudalis, and longissimus capitis, is closely related to horizontal eye position in the orbit both during spontaneous eye movements and vestibular nystagmus. The activity of splenius also shows this relationship but the coupling is less tight, probably because of the postural function of this muscle.

Saccadic responses evoked by presentation of visual and auditory targets.

Abstract: Saccadic eye movements evoked by the presentation of visual and auditory targets were examined and compared. Differences were found either in the pattern of the saccadic response and in the characteristics of single saccades of the same amplitude. The longer latency and the higher percentage of multiple saccade responses in the auditory case were attributed to a more complex central processing, whereas the longer duration and the lower peak velocity of the saccades to auditory targets were attributed to reduced performances of the execution mechanism in the absence of vision.

Anatomical relationships of serotoninergic and noradrenalinergic projections with the GnRH system in septum and hypothalamus.

Abstract: Immunahistochemical double staining for gonadotropin releasing hormone (GnRH) and serotonin or dopamine-β-hydroxylase reveals close appositions of fibers which contain serotonin or norepinephrine to GnRH producing neurons in the septo-preoptic region. In the organum vasculosum of the lamina terminalis and in the median eminence extensive anatomical overlap exists in the distribution of GnRH and serotoninergic fibers but little of GnRH and noradrenalinergic fibers. It is proposed that serotonin plays a major role in the regulation of GnRH secretion via contacts in all of the regions studied and that the influence of norepinephrine on GnRH-secretion in the median eminence is exerted mainly via involvement of dopaminergic tuberoinfundibular neurons.

Neuronal interactions in the substantia nigra pars reticulata through axon collaterals of the projection neurons. An electrophysiological and morphological study.

Abstract: Substantia nigra pars reticulata (SNr) neurons, antidromically activated following stimulation of the dorsal thalamus and/or superior colliculus were intracellularly stained with HRP Light microscopic analysis revealed that the labeled SNr neurons have axon collaterals arborizing within SNr Axon collaterals of SNr neurons partially overlapped with the dendritic fields of their parent cells and also extended beyond the parent dendritic fields The labeled axon terminals did not closely appose the parent cell processes, suggesting that the collaterals most likely terminate on neurons other than the parent cell Electrical stimulation of either the thalamus or the superior colliculus induced monosynaptic and polysynaptic IPSPs in SNr cells The polysynaptic IPSPs evoked from thalamic stimulation disappeared following hemitransection of the brain just rostral to the thalamus while the monosynaptic IPSPs remained the same Since there are no known afferents from either thalamus or superior colliculus to SNr, we consider that these monosynaptic IPSPs are due to activation of the recurrent collaterals of SNr projection cells The results of this study indicate that projection neurons of SNr also have an inhibitory role within the SNr

The control of rapid limb movement in the cat. III. Agonist - antagonist coupling.

Abstract: Electromyographic (EMG) activity associated with rapid voluntary limb movements exhibits a characteristic "three burst pattern". The first burst is in the agonist muscle (AG1), the second is in the antagonist (ANT) and the third is again in the agonist (AG2). The present study was undertaken to determine whether ANT and AG2 reflect preprogrammed commands or responses to stretch consequent upon limb displacement. To answer this question EMG activity of agonist and antagonist muscles was examined in cats performing a tracking task. To dissociate centrally programmed muscular events from their intended mechanical consequences, isometric and anisometric conditions were presented in either a predictable or unpredictable sequence. A torque motor was used to control limb trajectory and to impose passive angular displacements. Whereas AG1 was present under both isometric and anisometric conditions, ANT and AG2 required limb displacement and were time locked to movement parameters. ANT occurred within 15 ms following the onset of acceleration. its magnitude varied linearly with this parameter and inversely with AG1. Passive displacements stretching the antagonist elicited responses with similar latencies and greatest magnitude for a given acceleration. AG2 was only present in underdamped movements with terminal oscillations and typically occurred when the position reached its peak and the velocity recrossed zero. Its magnitude was a function of both limb deceleration and of intended force. The data indicate that both ANT and AG2 represent responses to muscles stretch whose amplitudes are modulated by descending commands. Reciprocal mechanisms operating at a spinal level could account for the reduction of the antagonist response as a function of intended force. The increased sensitivity of late stretch responses in the agonist with higher intended forces is compatible with motoneuron facilitation by tonic descending commands. It is proposed that the stretch evoked responses function to dampen terminal oscillations which ensue from rapid displacement of the mass of the limb against elastic forces of muscle and soft tissue.

Development and change of cortical field potentials during learning processes of visually initiated hand movements in the monkey.

Abstract: Field potentials on the surface and at 2.5–3.0 mm depth in the cerebral cortex were recorded in various areas with chronically implanted electrodes and the potentials which preceded hand movements in response to a light stimulus were observed during the process of learning the skilled conditioned movement. A naive monkey had to lift a lever by wrist extension within duration of the light stimulus lasting for 900, 700 or 510 ms depending on the stage of the learning process.

Connections of the hippocampal formation, mamillary bodies, anterior thalamus and cingulate cortex. A retrograde study using horseradish peroxidase in the cat

Abstract: The afferent projections to, and the interconnections between, four structures of the so-called limbic system were investigated in the cat. The retrograde horseradish peroxidase (HRP) technique was used to trace the origins of fibers projecting to each of these four loci. Particular emphasis was laid on tracing cortical afferents of these regions. Four injections were performed in the dorsal and two in the ventral subicular regions; six were centered within the mamillary nuclei, four within the anterior thalamic nuclei, and three within the cingulate gyrus. For each region, a number of projections were found which had apparently not been described before, at least not for the cat: For injections into the subicular regions, a hitherto unknown number of cortical afferents was detected, including labeled cells in the prefrontal and premotor fields and from large areas within the posterior parietal, temporal and occipital cortex (i.e., sensory and sensory integration cortex); numerous neurons were labeled in the anterior nuclear group of the thalamus. Injections of HRP into the mamillary nuclei revealed, aside from a strong projection from the subicular regions, frontocortical and cingulate projections to the mamillary nuclei; the mamillary nuclei also received subcortical projections from the septum, the diagonal band of Broca and from the periaqueductal gray. Following injections into the anterior thalamic nuclei, labeled cells were found in the prefrontal cortex, and to a lesser extent in lateral parts of the cortical hemisphere; subcortically, the mamillary nuclei received connections from hypothalamic areas, the periaqueductal gray, the diagonal band of Broca and the claustrum. Cingulate injections labeled cells in temporal and parietal cortical areas, in the subicular region, and also in the periaqueductal gray. Our findings reveal that each of the four injected areas receives a large number of afferents from divergent regions of the brain; of these, a considerable number is shared by each of the four injection loci. Furthermore, the present results reveal that the subiculum, the mamillary bodies, and the anterior thalamus are more strongly interconnected than previously assumed.

Cerebellar nuclear topography of simple and synergistic movements in the alert baboon (Papio papio).

Abstract: Movements elicited by the stimulation of the cerebellar nuclei were studied in alert baboons chronically prepared. The motor responses were filmed and recorded in eight muscles through chronically implanted electrodes. Two types of motor effects were observed: (1) Simple movements that concerned the unidirectional displacement of a limb segment. (2) Complex movements that involved distinct and frequently noncontiguous muscles were stereotyped and could not be dissociated. These movements are defined as motor synergies. Electromyographic study allowed us to investigate the motor response latencies and the modality of cerebellar control on musculature. Simple movements were due to the activation of muscles within the involved segment in addition to the co-contraction of muscles of a nearby segment. Thus they could be due to a cerebellar control over muscular synergies. Complex movements would correspond to the simultaneous activation of distinct muscular groups and could also be the outcome of a cerebellar control on motor synergies. Thus the effects of the interposed nucleus concern preferably flexor muscles whereas the effects of the dentate nucleus appear to be equally distributed among flexor and extensor muscles. Somatotopic motor localization were evidenced both in the interposed and dentate nuclei: there are somatotopic relations between every region of the interposed nucleus and musculature. As regards the dentate nucleus, two subdivisions were distinguished according to the complexity of elicited motor effects: (A) an antero-medial region from which motor synergies can be elicited. (B) a postero-lateral region giving rise to simple movements, mainly hand movements.

Single cell responses in cat visual cortex to visual stimulation during iontophoresis of noradrenaline.

Abstract: We studied how iontophoresis of noradrenaline (NA) changes responsiveness of individual cells in the feline visual cortex when their visual receptive fields are stimulated with the appropriate visual stimulus. We found three populations of cortical cells which either increased, decreased or did not change their visual responsiveness during NA iontophoresis. About equal numbers of cells belonged to each of these three groups. In the majority of such cells that changed visual responsiveness during NA iontophoresis and that had measurable amounts of spontaneous activity, the ratio of visually evoked to spontaneous activity (signal-to-noise ratio) improved during NA iontophoresis. This improvement was independent of the direction of changes in the response magnitude to visual stimulation. There was a differential effect of NA on simple and complex visual cortical cells: Although most simple cells (86%) clearly changed their responsiveness during NA iontophoresis, the effects were seen in only one-third of complex cells. Furthermore, the effects on complex cells were usually weak compared to those typically seen in simple cells. In some cases the effects of NA were more complicated than an overall enhancement or suppression of the cortical cell's responses to visual stimulation. The possible dual role of NA in the visual cortex is briefly discussed.

Characterization of the human auditory cortex by the neuromagnetic method.

Abstract: Neuromagnetic studies show that the location of cortical activity evoked by modulated tones and by click stimuli in the steady state paradigm can be determined non-invasively with a precision of a few millimeters. The progression of locations for tones of increasing frequency establish an orderly tonotopic map in which the distance along the cortex varies as the logarithm of the frequency. The active region responding to clicks lies at a position that is consistent with this map if the stimulus is characterized by the frequency of the peak of its power spectrum. A latency of about 50 ms observed for the response to clicks is in close correspondance with a strong component of the transient response to an isolated click reported in the literature. Monaural stimulation of the ear contralateral to the hemisphere being monitored produces a latency which is about 8 ms shorter than stimulation of the ipsilateral ear, in agreement with previous studies of transient responses. The amplitudes of the responses for binaurally presented clicks for sleeping subjects is substantially diminished for repetition rates above 20 Hz but is enhanced for lower rates.