Showing papers on "Thalamus published in 1993"
TL;DR: A unified scenario of the genesis of the three major sleep rhythms: slow, delta, and spindle oscillations is proposed.
Abstract: As most afferent axons to the thalamus originate in the cerebral cortex, we assumed that the slow (
702 citations
01 Jan 1993
TL;DR: In this article, the authors assumed that the slow (< 1 Hz) cortical oscillation described in the two companion articles is reflected in reticular (RE) thalamic and thalamocortical cells and hypothesized that the cortically generated slow rhythm would appear in the thalamus in conjunction with delta and spindle oscillations arising from intrinsic and network properties of RE neurons.
Abstract: As most afferent axons to the thalamus originate in the cerebral cortex, we assumed that the slow (< 1 Hz) cortical oscillation described in the two companion articles is reflected in reticular (RE) thalamic and thalamocortical cells. We hypothesized that the cortically generated slow rhythm would appear in the thalamus in conjunction with delta and spindle oscillations arising from intrinsic and network properties of thalamic neurons. Intracellular recordings have been obtained in anesthetized cats from RE (n = 51) and cortically projecting (n = 240) thalamic neurons. RE cells were physiologically identified by cortically evoked high-frequency spike bursts and depolarizing spindle oscillations. Thalamocortical cells were recognized by backfiring from appropriate neocortical areas, spindle-related cyclic IPSPs, and hyperpolarization-activated delta oscillation consisting of rhythmic low-threshold spikes (LTSs) alternating with afterhyperpolarizing potentials (AHPs). The slow rhythm (0.3-0.5 Hz) was recorded in 65% of RE neurons. In x90% of oscillating cells, the rhythm consisted of prolonged depolarizations giving rise to trains of single action potentials. DC hyperpolarization increased the synaptic noise and, in a few cells, suppressed the long-lasting depolarizing phase of the slow rhythm, without blocking the fast EPSPs. In -10% of oscillating neurons, the hyperpolarizing phase of the oscillation was much more pronounced, thus suggesting that the slow rhythm was produced by inhibitory sculpturing of the background firing. The slow oscillation was associated with faster rhythms (4-6 Hz) in the same RE neuron. The slow rhythm of RE neurons was closely related to EEG wave complexes recurring with the same frequency, and its strong dependency upon a synchronized state of cortical EEG was observed during shifts in EEG patterns at different levels of anesthesia. In 44% of thalamocortical cells the slow rhythm of depolarizing sequences was apparent and it could coexist with delta or spindle oscillations in the same neuron. The occurrence of the slowly recurring depolarizing envelopes was
685 citations
TL;DR: Specific roles of mGluR2 in the glutamatergic system in the brain is indicated, as seen in Golgi cells of the cerebellum and in the lower brainstem.
523 citations
TL;DR: Neurons throughout a broad expanse of cortex were highly responsive to pure tones, and best frequencies could be determined for neurons in arrays of recording sites, as well as two systematic representations of tone frequencies.
Abstract: Microelectrode recordings were used to investigate the tonotopic organization of auditory cortex of macaque monkeys and guide the placement of injections of wheat germ agglutinin-horse radish peroxidase (WGA-HRP) and fluorescent dyes. Anatomical and physiological results were later related to histological distinctions in the same brains after sections were processed for cytoarchitecture, myeloarchitecture, acetylcholinesterase (AchE), or cytochrome oxidase (CO). The experiments produced several major findings. (1) Neurons throughout a broad expanse of cortex were highly responsive to pure tones, and best frequencies could be determined for neurons in arrays of recording sites. (2) The microelectrode recordings revealed two systematic representations of tone frequencies, the primary area (AI) and a primary-like rostral field (R) as previously described. The representation of high to low frequency tones in A1 was largely caudorostral along the plane of the sulcus. A reversal of the order of representation of frequencies occurred in R. (3) AI and R together were coextensive with a koniocellular, densely myelinated zone that expressed high levels of AchE and CO. These architectonic features were somewhat less pronounced in R than AI, but a clear border between the two areas was not apparent. (4) Cortex bordering AI and R was less responsive to tones, but when best frequencies for neurons could be determined, they matched those for adjoining parts of AI and R. (5) Architectonically distinct regions were apparent within some of the cortex bordering AI and R. (6) The major ipsilateral cortical connections of AI were with R and cortex immediately lateral and medial to AI. (7) Callosal connections of AI were predominantly with matched locations in the opposite AI, but they also included adjoining fields. (8) Neurons in the ventral (MGV), medial (MGM), and dorsal (MGD) nuclei of the medial geniculate complex projected to AI and cortex lateral to AI. (9) Injections in cortex responsive to high frequency tones labeled more dorsal parts of MGV than injections in cortex responsive to low frequency tones.
482 citations
TL;DR: The organization of interconnections between the mediodorsal nucleus of the thalamus (MD) and the orbital and medial prefrontal cortex and the agranular insular cortex in the monkey was studied by retrograde and anterograde tracing techniques.
Abstract: The organization of interconnections between the mediodorsal nucleus of the thalamus (MD) and the orbital and medial prefrontal cortex and the agranular insular cortex in the monkey was studied by retrograde and anterograde tracing techniques. In addition to the magnocellular and parvicellular divisions of MD, three other subdivisions can be recognized on the basis of myeloarchitecture, cytoarchitecture, and connections. The first two of these represent a parcellation of the magnocellular division into a lateral, fiber-rich MD pars fibrosa and a medial, poorly myelinated MD pars paramediana adjacent to the midline. The third is a small, poorly myelinated area located at the caudomedial and dorsal edges of MD; it is referred to as MD pars caudodorsalis. MD pars fibrosa is reciprocally interconnected primarily with areas 11, 12 and 13 in the central and lateral part of the orbital cortex. There is a general organization within this projection, with the rostrocaudal axis of the cortex represented from dorsal to ventral in the pars fibrosa, and the mediolateral cortical axis represented from medial to lateral. Cells that project to area 12 also extend laterally into the adjacent pars parvicellularis. MD pars paramediana is more heavily interconnected with the caudal and medial portions of the orbital region, particularly the agranular insular areas and the caudal parts of areas 13 and 14. Cells that project to two caudal areas, 13a and Iad, do not fit with the general organization, in that they are located in the dorsomedial parts of the pars fibrosa and pars paramediana, where they overlap with cells that project to area 14. The pars fibrosa and pars paramediana receive inputs from areas of the ventral forebrain such as the amygdala, piriform (olfactory) cortex, and entorhinal cortex, which project directly to the orbital and agranular insular cortex, as well as from the ventral pallidum. MD pars caudodorsalis is reciprocally interconnected with areas 14, 24, and 32 on the medial surface of the prefrontal cortex. In this part of the nucleus the dorsoventral axis of the medial prefrontal cortex is represented from caudal to rostral in the thalamus. The amygdala and other ventral forebrain structures do not send fibers into the pars caudodorsalis, even though some of these structures project directly to the medial prefrontal cortex. Ventral to MD, and separated from it by the internal medullary lamina, a small region was recognized that appears to be comparable to the anteroventral part of the submedial nucleus previously defined in the rat and cat.(ABSTRACT TRUNCATED AT 400 WORDS)
393 citations
TL;DR: In situ hybridization is used to compare the regional and cellular distributions of the two GAD mRNAs in rat brain to provide more flexibility in the regulation of GABA synthesis than either GAD65 and GAD67 together may provide.
Abstract: Two genes encode two forms of glutamate decarboxylase, GAD65 and GAD67. Because the two GADs differ in subcellular distribution and interactions with the cofactor pyridoxal phosphate, the two enzymes may play different roles in gamma-aminobutyric acid (GABA) production. In this study we have used in situ hybridization to compare the regional and cellular distributions of the two GAD mRNAs in rat brain. Both GAD mRNAs are abundant in olfactory bulb, olfactory tubercle, zona incerta, reticular nucleus of the thalamus, oculomotor nuclei, and pontine tegmental area. GAD65 mRNA is more abundant in several structures of the visual system, including the lateral geniculate nuclei, superior colliculi, and olivary pretectal nucleus, as well as in several hypothalamic and pontine nuclei. In contrast, GAD67 mRNA is more abundant in neocortex, the granular layer of olfactory bulb, lateral and medial septum, globus pallidus, inferior colliculi, and cerebellar cortex. Both GAD mRNAs are present in interneurons as well as in projection neurons, and both are present in neurons with different types of synapses, including dendrodendiritic, axosomatic, and axodendritic synapses. GAD65 mRNA predominates in the visual and the neuroendocrine systems, which are more subject to phasic changes, while GAD67 is present at relatively higher concentrations in many tonically active neurons. GAD65 and GAD67 together may provide more flexibility in the regulation of GABA synthesis than either could alone. © 1993 Wiley-Liss, Inc.
291 citations
TL;DR: The demonstration of reactive microglia indicates not only imminent ischemic neuronal damage within MCA territory but can also delineate extra‐focal disturbances, possibly reflecting subtle and transitory changes in neuronal activity.
Abstract: We have studied the microglial reaction that accompanies cortical infarction induced by middle cerebral artery occlusion (MCAO). Lectin histochemistry with the B4-isolectin from Griffonia simplicifolia as well as immunocytochemistry with a panel of monoclonal antibodies directed against major histocompatibility complex (MHC) and lymphocytic antigens were performed. Principal attention was focused on neocortical and thalamic regions, representative of primary and secondary ischemic damage, respectively. With the lectin procedure, activated microglial cells were abundant in the neocortex 24 hours after MCAO. In contrast, microglial activation in the thalamus was not apparent until day 2 after MCAO. On day 5, MHC class II antigen was expressed by reactive microglia in fiber tracts traversing the striatum, but was absent from activated microglia in the primary cortical infarction area. MHC class I and lymphocytic antigens were expressed differentially on microglia with class I antigens appearing early and lymphocytic antigens appearing late in the time course after focal ischemia. The findings are compatible with previous studies during global ischemia and confirm the early activation and the progressive nature of immunomolecule expression on activated microglia after an ischemic insult. In addition to neocortical and thalamic sites, our results showed an early microglial activation to be present also in forebrain regions outside of the middle cerebral artery (MCA) territory, such as the contralateral cortex and hippocampus. A unilateral microglial reaction was also detectable after long-term survival (> or = 4 weeks) in the pyramidal tracts, as well as in the corticospinal tracts at cervical but not lumbar spinal cord levels. Ischemia-induced neuronal damage, as evaluated by Nissl staining, was found only in cortical and thalamic regions. We conclude that the demonstration of reactive microglia indicates not only imminent ischemic neuronal damage within MCA territory but can also delineate extra-focal disturbances, possibly reflecting subtle and transitory changes in neuronal activity.
262 citations
TL;DR: A general requirement for subplate neurons throughout neocortex in the process of cortical target selection and ingrowth by thalamic axons is underscored.
Abstract: During cerebral cortical development, ingrowing axons from different thalamic nuclei select and invade their cortical targets. The selection of an appropriate target is first evident even before thalamic axons grow into the cortical plate: initially axons accumulate and wait below their cortical target area in a zone called the subplate. This zone also contains the first postmitotic neurons of the cerebral cortex, the subplate neurons. Here we have investigated whether subplate neurons are involved in the process of target selection by thalamic axons by ablating them from specific cortical regions at the onset of the waiting period and examining the subsequent thalamocortical axon projection patterns. Subplate neurons were ablated at the onset of the waiting period by intracortical injections of kainic acid. The effect of the ablation on the thalamocortical projection from visual thalamus was examined by DiI-labeling of the LGN days to weeks following the lesion. At two to four weeks post-lesion, times when LGN axons would have normally invaded the cortical plate, the axons remained below the cortical plate and grew past their appropriate cortical target in an anomalous pathway. Moreover, examination of LGN axons at one week post-lesion, a time when they would normally be waiting and branching within the visual subplate, indicated that the axons had already grown past their correct destination. These observations suggest that visual subplate neurons are involved in the process by which LGN axons select and subsequently grow into visual cortex. In contrast, subplate neurons do not appear to play a major role in the initial morphological development of the LGN itself. Subplate ablations did not alter dendritic growth or shapes of LGN projection neurons during the period under study, nor did it prevent the segregation of retinal ganglion cell axons into eye-specific layers. However, the overall size of the LGN was reduced, suggesting that there may be increased cell death of LGN neurons in the absence of subplate neurons. To examine whether subplate neurons beneath other neocortical areas play a similar role in the formation of thalamocortical connections, subplate neurons were deleted beneath auditory cortex at the onset of the waiting period for auditory thalamic axons. Subsequent DiI labeling revealed that in these animals the majority of MGN axons had grown past auditory cortex instead of innervating it. Taken together these observations underscore a general requirement for subplate neurons throughout neocortex in the process of cortical target selection and ingrowth by thalamic axons.(ABSTRACT TRUNCATED AT 400 WORDS)
254 citations
TL;DR: Cortical and thalamic projections to the frontal eye fields and posterior parietal cortex do not represent axonal collaterals of single neurons but originate from two distinct and partially overlapping populations of neurons.
Abstract: The spatial distribution of directed attention is coordinated by a large-scale neural network. The three principal cortical components of this network are located in the region of the frontal eye fields, posterior parietal cortex, and the cingulate cortex. We injected a retrogradely transported fluorescent dye into the frontal eye fields and another into the posterior parietal cortex of the monkey brain. Large numbers of neurons in the cingulate cortex were retrogradely labeled with each of the two fluorescent dyes. The two types of retrogradely labeled neurons were extensively intermingled, but neurons labeled with both tracers constituted less than 1% of retrogradely labeled cingulate neurons. Other cortical areas that contained retrograde neuronal labeling included the premotor, lateral neuronal labeling included the premotor, lateral prefrontal, orbitofrontal, opercular, posterior parietal, lateral temporal, inferior temporal, parahippocampal, and insular regions. These areas contained neurons labeled with each of the two dyes but virtually no neurons labeled with both. In the thalamus, retrogradely labeled nuclei failed to display evidence of double labeling. The overlap between the two populations of retrogradely labeled neurons was far more extensive at the cortical than at the thalamic level. These observations show that cortical and thalamic projections to the frontal eye fields and posterior parietal cortex do not represent axonal collaterals of single neurons but originate from two distinct and partially overlapping populations of neurons.
234 citations
TL;DR: Thalamic reorganization demonstrates that peripheral sensory deprivation may induce immediate plastic changes at multiple levels of the somatosensory system, and suggests a disruption of the normal dynamic equilibrium between multiple ascending and descending influences on the VPM.
Abstract: PERIPHERAL sensory deprivation induces reorganization within the somatosensory cortex of adult animals1-6. Although most studies have focused on the somatosensory cortex1–6, changes at subcortical levels (for example the thalamus) could also play a fundamental role in sensory plasticity7–11. To investigate this, we made chronic simultaneous recordings of large numbers of single neurons across the ventral posterior medial thalamus (VPM) in adult rats. This allowed a continuous and quantitative evaluation of the receptive fields of the same sample of single VPM neurons per animal, before and after sensory deprivation. Local anaesthesia in the face induced an immediate and reversible reorganization of a large portion of the VPM map. This differentially affected the short latency (4–6 ms) responses (SLRs) and long latency (15–25 ms) responses (LLRs) of single VPM neurons. The SLRs and LLRs normally define spatiotemporally complex receptive fields in the VPM12. Here we report that 73% of single neurons whose original receptive fields included the anaesthetized zone showed immediate unmasking of SLRs in response to stimulation of adjacent cutaneous regions, and/or loss of SLRs with preservation or enhancement of LLRs in response to stimulation of regions just surrounding the anaesthetized zone. This thalamic reorganization demonstrates that peripheral sensory deprivation may induce immediate plastic changes at multiple levels of the somatosensory system. Further, its spatiotemporally complex character suggests a disruption of the normal dynamic equilibrium between multiple ascending and descending influences on the VPM.
TL;DR: The combined effects of NB stimulation served to increase cortical excitability and facilitate the ability of the EPSP to elicit action potentials, indicating that NB cholinergic neurons can modify neocortical functions by facilitating thalamocortical synaptic transmission.
Abstract: Nucleus basalis (NB) neurons are a primary source of neocortical acetylcholine (ACh) and likely contribute to mechanisms of neocortical activation. However, the functions of neocortical activation and its cholinergic component remain unclear. To identify functional consequences of NB activity, we have studied the effects of NB stimulation on thalamocortical transmission. Here we report that tetanic NB stimulation facilitated field potentials, single neuron discharges, and monosynaptic excitatory postsynaptic potentials (EPSPs) elicited in middle to deep cortical layers of the rat auditory cortex following stimulation of the auditory thalamus (medial geniculate, MG). NB stimulation produced a twofold increase in the slope and amplitude of the evoked short-latency (onset 3.0 ± 0.13 ms, peak 6.3 ± 0.21 ms), negative-polarity cortical field potential and increased the probability and synchrony of MG-evoked unit discharges, without altering the preceding fiber volley. Intracortical application of atropine blocked the NB-mediated facilitation of field potentials, indicating action of ACh at cortical muscarinic receptors. Intracellular recordings revealed that the short-latency cortical field potential coincided with a short-latency EPSP (onset 3.3 ± 0.20 ms, peak 5.6 ± 0.47 ms). NB stimulation decreased the onset and peak latencies of the EPSP by about 20% and increased its amplitude by 26%. NB stimulation also produced slow membrane depolarization and sometimes reduced a long-lasting IPSP that followed the EPSP. The combined effects of NB stimulation served to increase cortical excitability and facilitate the ability of the EPSP to elicit action potentials. Taken together, these data indicate that NB cholinergic neurons can modify neocortical functions by facilitating thalamocortical synaptic transmission. © 1993 Wiley-Liss, Inc.
TL;DR: It is concluded that the sensory and motor input to the cortex are subjected to a similar control mechanism, under frontal control, for the transmission of subcortical motor information to the cerebral cortex.
Abstract: In this paper the similarities in the structural and functional organization of motor preparation and attention are discussed. A crucial structure in this organization is the thalamus, a complex of sensory and motor nuclei that transmits information from subcortical origins to the cortex. For the most part, the thalamus is overlapped by the nucleus reticularis, which has a local inhibitory influence on the underlying nuclei. This serves as a gating mechanism for the transmission of sensory information to the cortex. Skinner and Yingling (1977) have provided arguments in favor of a frontal control in the gating of sensory information. The present paper extends their suggestions to the motor system: a similar gating mechanism for the transmission of subcortical motor information to the cortex is hypothesized, also under frontal control. Slow potentials recorded during motor preparation and attention for an upcoming stimulus show a different distribution over the scalp. These distributions are interpreted as an indication of which thalamic gates are open to transmit information to the cortex. Probe responses (spinal reflexes, evoked potentials, and the startle reflex) can also be used to investigate which thalamocortical gates are open under certain experimental conditions. It is concluded that the sensory and motor input to the cortex are subjected to a similar control mechanism. Language: en
TL;DR: Low metabolic rates were confirmed in medial frontal cortical regions as well as in the basal ganglia, consistent with the importance of the cortical-striatal-thalamic pathways in schizophrenia.
Abstract: OBJECTIVE The cortical-striatal-thalamic circuit modulates cognitive processing and thus may be involved in the cognitive dysfunction in schizophrenia. The imaging of metabolic rate in the structures making up this circuit could reveal the correlates of schizophrenia and its main symptoms. METHOD Seventy male schizophrenic patients underwent [18F]-fluorodeoxyglucose positron emission tomography after a period of at least 4 weeks during which they had not received neuroleptic medication and were compared to 30 age-matched male normal comparison subjects. RESULTS Analyses revealed decreased metabolism in medial frontal cortex, cingulate gyrus, medial temporal lobe, corpus callosum, and ventral caudate and increased metabolism in the left lateral temporal and occipital cortices in the schizophrenic cohort. Consistent with previous studies, the schizophrenic group had lower hypofrontality scores (ratios of lateral frontal to occipital metabolism) than did comparison subjects. The lateral frontal cortical metabolism of schizophrenic patients did not differ from that of comparison subjects, while occipital cortical metabolism was high, suggesting that lateral hypofrontality is due to abnormalities in occipital rather than lateral frontal activity. Hypofrontality was more prominent in medial than lateral frontal cortex. Brief Psychiatric Rating Scale (BPRS) scores, obtained for each schizophrenic patient on the scan day, were correlated with regional brain glucose metabolic rate. Medial frontal cortical and thalamic activity correlated negatively with total BPRS score and with positive and negative symptom scores. Lateral frontal cortical metabolism and hypofrontality scores did not significantly correlate with negative symptoms. Analyses of variance demonstrated a reduced right greater than left asymmetry in the schizophrenic patients for the lateral cortex as a whole, with simple interactions showing this effect specifically in temporal and frontal cortical regions. CONCLUSIONS Low metabolic rates were confirmed in medial frontal cortical regions as well as in the basal ganglia, consistent with the importance of the cortical-striatal-thalamic pathways in schizophrenia. Loss of normal lateralization patterns was also observed on an exploratory basis. Correlations with negative symptoms and group differences were more prominent in medial than lateral frontal cortex, suggesting that medial regions may be more important in schizophrenic pathology.
TL;DR: Six patients with unilateral Parkinson's disease had an electrode chronically implanted in the ventral intermediate nucleus of the thalamus and the results give evidence for different contributions from cortex and cerebellum to the generation of parkinsonian tremor.
Abstract: Parkinsonian tremor can be abolished by chronic high frequency thalamic stimulation of the ventral intermediate nucleus. We have studied six patients with unilateral Parkinson's disease. The patients had an electrode chronically implanted in the ventral intermediate nucleus of the thalamus. We measured changes in cerebral activity by positron emission tomography using an index of regional cerebral blood flow (rCBF). Each patient was scanned in three states: (i) tremor without stimulation (condition A); (ii) tremor with ineffective stimulation (condition B); (iii) tremor abolished by effective stimulation (condition C). The suppression of tremor (C compared with B) was specifically associated with a decrease of rCBF in the cerebellum, whereas the ineffective stimulation (B compared with A) induced a decrease of rCBF in homolateral cerebral cortex. The results give evidence for different contributions from cortex and cerebellum to the generation of parkinsonian tremor and suggest that tremor suppression is mainly associated with a decrease of synaptic activity in the cerebellum.
TL;DR: Evidence from the adult structure of the nucleus and ongoing developmental studies suggest that the reticular nucleus plays an important part in organizing the earliest connections between cortex and thalamus and that the developmental sequence may explain the complex connections formed in the adult.
TL;DR: TheForelimb area of the primary motor cortex receives both segregated and intermixed inputs from cortical and subcortical sources, indicating possible different functional roles of frontal premotor areas in control of coordinated distal and proximal forelimb movements.
Abstract: The present double-labeling study was designed to demonstrate the morphological framework for motor control in coordinated distal and proximal forelimb movements, which may partly, at least, depend on corticocortical and thalamocortical inputs to the forelimb area in the primary motor cortex. After intracortical microstimulation mapping of the forelimb area in the primary motor cortex of four macaque monkeys, a retrograde tracing study with fluorescent dyes was attempted to label simultaneously neurons in cortical and subcortical sites projecting to the distal forelimb representation area and those projecting to the proximal representation area of the primary motor cortex. Neurons projecting to distal and proximal forelimb parts of the primary motor cortex were largely separate in the following areas: the premotor area, primary somatosensory area, secondary somatosensory area, area 5, and thalamus. In contrast, there was no precise topographic organization of labeled projection neurons in the following areas: the supplementary motor area, cingulate motor area, primary motor cortex adjacent to the injection sites, claustrum, and basal nucleus of Meynert. The present study revealed that the forelimb area of the primary motor cortex receives both segregated and intermixed inputs from cortical and subcortical sources. In particular, the fact that the forelimb area of the primary motor cortex receives topographically organized inputs from the premotor area and nontopographically organized inputs from the supplementary motor area and cingulate motor area indicates possible different functional roles of frontal premotor areas in control of coordinated distal and proximal forelimb movements. © 1993 Wiley-Liss, Inc.
TL;DR: The early appearance of the thalamocortical pathway is consistent with an organizational role in the specification of some features of cortical cytoarchitecture and strongly suggests the recognition of particular cortical regions.
Abstract: The early development of thalamocortical and corticothalamic projections in hamsters was studied to compare the specificity and maturation of these pathways, and to identify potential sources of information for specification of cortical areas. The cells that constitute these projections are both generated prenatally in hamsters and they make reciprocal connections. Fluorescent dyes (DiI and DiA) were injected into the visual cortex or lateral geniculate nucleus in fixed brains of fetal and postnatal pups. Several issues in axonal development were examined, including timing of axon outgrowth and target invasion, projection specificity, the spatial relationship between the two pathways, and the connections of subplate cells. Thalamic projections arrive in the visual cortex 2 days before birth and begin to invade the developing cortical plate by the next day. Few processes invade inappropriate cortical regions. By postnatal day 7 their laminar position is similar to mature animals. By contrast, visual cortical axons from subplate and layer 6 cells reach posterior thalamus at 1 day after birth in small numbers. By 3 days after birth many layer 5 cell projections reach the posterior thalamus. On postnatal day 7, there is a sudden increase in the number of layer 6 projections to the thalamus. Surprisingly, these layer 6 cells are precisely topographically mapped with colabeled thalamic afferents on their first appearance. Subplate cells constitute a very small component of the corticothalamic projection at all ages. Double injections of DiI and DiA show that the corticofugal and thalamocortical pathways are physically separate during development. Corticofugal axons travel deep in the intermediate zone to the thalamic axons and are separate through much of the internal capsule. Their tangential distribution is also distinct. The early appearance of the thalamocortical pathway is consistent with an organizational role in the specification of some features of cortical cytoarchitecture. The specific initial projection of thalamocortical axons strongly suggests the recognition of particular cortical regions. The physical separation of these two pathways limits the possibility for exchange of information between these systems except at their respective targets.
TL;DR: The data suggest that glaucoma leads to greater loss of magnocellular tissue at the level of the lateral geniculate, as well as to its mag nocellular and parvocellular layers.
TL;DR: The results indicate that both areas TE and TEO receive nonreciprocal inputs from several thalarnic nuclei, including paracentralis, ventralis anterior, centralis, and limitans, and that TE also receives input from reuniens.
Abstract: To investigate the subcortical connections of inferior temporal cortex, we injected its anterior and posterior portions (Bonin and Bailey's cytoarchitectonic areas TE and TEO, respectively) in 6 rhesus monkeys with retrograde and anterograde tracers. The results indicate that both areas TE and TEO receive nonreciprocal inputs from several thalamic nuclei, including paracentralis, ventralis anterior, centralis, and limitans, and that TE also receives input from reuniens. Additional nonreciprocal inputs to both areas arise from the hypothalamus, basal nucleus of Meynert, dorsal and median raphe, locus coeruleus, and reticular formation. TE and TEO are reciprocally connected with the lateral, medial, and inferior nuclei of the pulvinar and with the ventral portion of the claustrum. The main subcortical nonreciprocal output from TE and TEO is to the striatum and from TEO to the superior colliculus. TE also sends a very limited projection to nucleus medialis dorsalis magnocellularis of the thalamus. Although the connections of areas TE and TEO are overlapping in most subcortical structures, they are partially segregated in the pulvinar, the reticular nucleus of the thalamus, and the striatum. Specifically, relative to those of TE, the projections of TEO are located more laterally in the medial, lateral, and inferior nuclei of the pulvinar, more ventrally in the reticular nucleus, and more caudally in both the ventral putamen and tail and head of the caudate nucleus.
TL;DR: It is now clear that higher primates have four strip-like representations of skin and muscle receptors corresponding to areas 3 a, 3b, 1 and 2 of anterior parietal cortex.
Abstract: Our understanding of the functional organization of somatosensory cortex and thalamus in primates and other mammals has greatly increased over the last few years. It is now clear that higher primates have four strip-like representations of skin and muscle receptors corresponding to areas 3 a, 3b, 1 and 2 of anterior parietal cortex. Areas 3b and 1 receive cutaneous information from the ventroposterior nucleus, while a ventroposterior superior nucleus provides areas 3a and 2 with information from muscle receptors. Area 3b is the homolog of S-I in prosimians and non-primates and it provides most of the activating cutaneous inputs to areas 1 and 2. Most of the further processing that allows tactile recognition of objects involves somatosensory areas of the lateral sulcus, where both S-II and the parietal ventral area (PV) receive activating inputs from areas 3a, 3b, 1 and 2. S-II also projects to PV and to a parietal rostral area where further connections with the amygdala and hippocampus may occur to allow the formation of tactile memories. Areas of anterior parietal cortex also project to posterior parietal cortex, where regions of cortex are largely somatosensory, but the functional subdivisions remain uncertain. All of the somatosensory fields have access to motor areas of the frontal lobe, but the magnitude and targets of the projections differ.
TL;DR: A possible role for certain neurons in the brain's early reaction to a penetrating injury is suggested, including the early and marked presence of tumor necrosis factor-α and interleukin-1α in neuronal somata of the striatum following a surgical injury to the hippocampus.
TL;DR: These connectional differences, compared with the pattern of organization of the motor cortical areas in primates, suggest that RFA in the rat may well be an equivalent of the premotor or supplementary motor area.
Abstract: The existence of multiple motor cortical areas that differ in some of their properties is well known in primates, but is less clear in the rat. The present study addressed this question from the point of view of connectional properties by comparing the afferent and efferent projections of the caudal forelimb area (CFA), considered to be the equivalent of the forelimb area of the primary motor cortex (MI), and a second forelimb motor representation, the rostral forelimb area (RFA). As a result of various tracing experiments (including double labeling), it was observed that CFA and RFA had reciprocal corticocortical connections characterized by preferential, asymmetrical, laminar distribution, indicating that RFA may occupy a different hierarchical level than CFA, according to criteria previously discussed in the visual cortex of primates. Furthermore, it was found that RFA, but not CFA, exhibited dense reciprocal connections with the insular cortex. With respect to their efferent projection to the basal ganglia, it was observed that CFA projected very densely to the lateral portion of the ipsilateral caudate putamen, whereas the contralateral projection was sparse and more restricted. The ipsilateral projection originating from RFA was slightly less dense than that from CFA, but it covered a larger portion of the caudate putamen (in the medial direction); the contralateral projection from RFA to the caudate putamen was of the same density and extent as the ipsilateral projection. The reciprocal thalamocortical and corticothalamic connections of RFA and CFA differed from each other in the sense that CFA was mainly interconnected with the ventrolateral thalamic nucleus, while RFA was mainly connected with the ventromedial thalamic nucleus. Altogether, these connectional differences, compared with the pattern of organization of the motor cortical areas in primates, suggest that RFA in the rat may well be an equivalent of the premotor or supplementary motor area. In contrast to the corticocortical, corticostriatal, and thalamocortical connections, RFA and CFA showed similar efferent projections to the subthalamic nucleus, substantia nigra, red nucleus, tectum, pontine nuclei, inferior olive, and spinal cord.
TL;DR: The INC is the most rostral brainstem structure mediating eye-head coordination in roll as well as thalamic ischemia, which is responsible for the tonic effects on vestibular function in the roll plane.
Abstract: We determined the subjective visual vertical (SVV), ocular torsion (OT), skew deviation, and lateral head tilt in 35 patients with acute thalamic infarctions (14 paramedian, 17 posterolateral, and four anterior polar) and in five patients with mesodiencephalic hemorrhages to obtain the tonic effects on vestibular function in the roll plane. Eight of 14 paramedian infarctions had complete ocular tilt reaction (OTR) with contraversive head tilt, skew deviation, OT, and SVV tilt. The OTR was due to ischemia of the rostral midbrain tegmentum, including the interstitial nucleus of Cajal (INC), and not to thalamic ischemia. Thus, the INC (and the rostral interstitial nucleus of the medial longitudinal fascicle) is the most rostral brainstem structure mediating eye-head coordination in roll. Eleven of 17 posterolateral infarctions exhibited moderate SVV tilts that were either ipsiversive or contraversive. In these 11 cases, vestibular thalamic nuclei (nucleus ventro-oralis intermedius, nucleus ventrocaudalis externus, and nucleus dorsocaudalis) were involved; infarctions in the remaining six were more ventromedial. Anterior polar infarctions did not affect vestibular function in roll.
TL;DR: It is proposed that neurogenic pain is due to an imbalance between central lateral and ventroposterior nuclei, resulting in an overinhibition of both by the thalamic reticular nucleus.
Abstract: Microelectrode recordings in the medial thalamus of 45 neurogenic pain patients undergoing medial thalamotomy revealed that most units (316/318) did not respond to somatosensory stimuli, and that half exhibited low-threshold calcium spike bursts. After medial thalamotomy, 67% of the patients reached a 50 to 100% pain relief, without somatosensory deficits. Colocalization of bursting activities and of the most efficient therapeutic lesions in the central lateral nucleus suggests a key role of this structure in neurogenic pain. We propose that neurogenic pain is due to an imbalance between central lateral and ventroposterior nuclei, resulting in an overinhibition of both by the thalamic reticular nucleus.
TL;DR: Regional changes in brain neural activity were examined in rats with painful peripheral mononeuropathy by using the fully quantitative 14C-2-deoxyglucose (2-DG) autoradiographic technique to measure local glucose utilization rate to reflect brain neural processing of spontaneous pain.
Abstract: Regional changes in brain neural activity were examined in rats with painful peripheral mononeuropathy (chronic constrictive injury, CCI) by using the fully quantitative 14C-2-deoxyglucose (2-DG) autoradiographic technique to measure local glucose utilization rate. CCI rats used in the experiment exhibited demonstrable thermal hyperalgesia and spontaneous pain behaviors 10 d after sciatic nerve ligation when the 2-DG experiment was carried out. In the absence of overt peripheral stimulation, reliable increases in 2-DG metabolic activity were observed in CCI rats as compared to sham-operated rats within extensive brain regions that have been implicated in supraspinal nociceptive processing. These brain regions included cortical somatosensory areas, cingulate cortex, amygdala, ventral posterolateral thalamic nucleus, posterior thalamic nucleus, hypothalamic arcuate nucleus, central gray matter, deep layers of superior colliculus, pontine reticular nuclei, locus coeruleus, parabrachial nucleus, gigantocellular reticular nucleus, and paragigantocellular nucleus. The increase in 2-DG metabolic activity was bilateral in most brain regions of CCI rats. However, somatosensory regions within the thalamus and the cerebral cortex were activated in CCI rats. High levels of 2-DG metabolic activity were observed within the cortical hind limb area, ventral posterolateral thalamic nucleus, and posterior thalamic nucleus contralateral to the ligated sciatic nerve, and these levels were higher than ipsilateral corresponding regions in CCI rats. In addition, patterns of increased neural activity found in the brain of CCI rats showed some similarities and differences to those found in the brain of rats exposed to acute nociception induced by noxious heat or formalin stimulation. Thus, these CCI-induced spontaneous increases in neural activity within extensive brain regions of CCI rats previously implicated in sensory-discriminative and affective-motivational dimensions of pain as well as centrifugal modulation of pain are likely to reflect brain neural processing of spontaneous pain. Implications of increased brain neural activity in mechanisms of neuropathic pain are discussed with emphasis on correlations between spatial patterns of altered brain neural activity and pain-related behaviors in CCI rats and clinical symptoms in neuropathic pain patients.
TL;DR: In cat dorsal column nuclei (DCN), the injection of local anesthetic into the receptive fields of DCN neurons resulted in the emergence of a new receptive field in all 13 neurons studied, indicating mechanisms underlying somatotopic reorganization exist at the earliest stages of somatosensory processing.
Abstract: Altered sensory input can result in the reorganization of somatosensory maps in the cerebral cortex and thalamus, but the extent to which reorganization occurs at lower levels of the somatosensory system is unknown. In cat dorsal column nuclei (DCN), the injection of local anesthetic into the receptive fields of DCN neurons resulted in the emergence of a new receptive field in all 13 neurons studied. New receptive fields emerged rapidly (within minutes), sometimes accompanied by changes in adaptation rates and stimulus selectivity, suggesting that the new fields arose from the unmasking of previously ineffective inputs. Receptive field reorganization was not imposed by descending cortical inputs to the DCN, because comparable results were obtained in 10 additional cells when the somatosensory and motor cortex were removed before recording. These results suggest that mechanisms underlying somatotopic reorganization exist at the earliest stages of somatosensory processing. Such mechanisms may participate in adaptive responses of the nervous system to injury or continuously changing sensory stimulation.
TL;DR: Direct evidence for the involvement of the anterior thalamic nuclei in memory processes emerges from two experiments with rats that examined performance of a spatial test of working memory, delayed nonmatching-to-position, and showed that lesions of the fornix and removal of the hippocampus produced very similar deficits.
TL;DR: In epilept WAG/Rij rats, multiple unit activity coinciding with the occurrence of spike-wave discharges was recorded under neurolept anesthesia and it is suggested that those thalamic nucleic thought to be involved in the production of cortical spindles are mediated in the genesis of the latter activity.
TL;DR: The results indicate that reward-related processes, as measured in the place preference conditioning paradigm, may depend upon ventral striatopallidal outflow that engages medial dorsal thalamus-frontal cortex mechanisms, in addition to the previously highlighted direct outflow to brainstem elements of the motor system.