Somatosensory system

About: Somatosensory system is a research topic. Over the lifetime, 6371 publications have been published within this topic receiving 316900 citations.

Organization of the amygdalopetal projections from modality-specific cortical association areas in the monkey

Abstract: As part of an attempt to understand how sensory stimuli influence emotional processes we examined all of the telencephalic sensory systems of the rhesus monkey for efferents to the amygdala and immediately surrounding structures, using primarily the Fink-Heimer technique. The results support the following conclusions. 1. All sensory systems contain areas that project to the amygdaloid complex (the somatosensory system, tentatively so), but not to more central limbic structures in the basal forebrain and hypothalamus. Consequently, whatever influence the sensory systems have on emotional processes mediated by these more central limbic structures is likely to depend largely on relays through the amygdala. 2. Except for the olfactory system, the amygdalopetal projections arise only from the later stages of cortical processing within each sensory system, i.e., from the modality-specific association areas one or more steps removed from the primary sensory areas. Thus, the modality-specific cortical sources of the amygdalopetal projections, like their amygdaloid targets, are important links in the sensory-limbic pathways. These sources are: for vision, areas TE and ventral TG; for audition, anterior TA and dorsal TG; for taste, area IA; and for somesthesis, possibly areas IA or IB. The amygdalopetal sources thus occupy a limited territory that begins dorsally in the anterior insula and extends ventrally across the anterior temporal neocortex as far as the rhinal fissure. 3. Within the visual system, progressively heavier and more widespread efferents arise from successively later stages of the amygdalopetal sources. The posterior half of TE sends a moderate projection to the dorsal part of the lateral nucleus, the anterior half of TE sends a heavy projection to the dorsal parts of both the lateral and basal nuclei, and the ventral part of TG sends a heavy projection to the dorsal and medial parts of the lateral and basal nuclei and to the dorsal part of the basal accessory nucleus. This pattern of progressive intensification and spread of the amygdalopetal projections applies also to the auditory system and probably to the other cortical sensory systems as well. The pattern suggests that a progressively greater influence on amygdaloid activity is exerted by successively more highly processed sensory information. 4. The efferents to the amygdaloid complex from the different sensory systems terminate in a dovetailed pattern. The major amygdaloid targets are: for vision, the anterodorsal parts of the lateral, basal, and basal accessory nuclei; for audition, the posterior parts of the lateral and basal accessory nuclei; for taste, the medial parts of the lateral and basal nuclei; and for olfaction, the cortical and medial nuclei. This pattern implies that each part of the amygdala is under the major influence of a particular sensory system. 5. The same cortical areas that give rise to separate sensory channels to the amygdala send efferents that converge upon the perirhinal and prorhinal cortices, areas known to be a major source of input to the hippocampus. Consequently, both the amygdala and hippocampus can be activated by the same highly processed sensory information, a conclusion that may help to account for a recent finding that these two structures can substitute for each other in a mechanism for recognition memory.

Responses to visual stimulation and relationship between visual, auditory, and somatosensory inputs in mouse superior colliculus.

Abstract: The superior colliculus was studied in anesthetized mice by recording from single cells and from unit clusters. The topographic representation of the visual filed was similar to what has been found in other mammals, with the temporal part of the contralateral visual field projecting posteriorly and the inferior visual field projecting laterally. At the anterior margin of the tectum receptive fields recorded through the contralateral eye and invaded the ipsilateral visual hemifield for up to 35 degrees, suggesting that the entire visual field through one eye is represented on the contralateral superior colliculus. Cells located closest to the tectal surface had relatively small receptive fields, averaging 9 degrees in center diameter; field sizes increased steadily with depth. The prevailing cell type in the stratum zonal and superficial gray responded best to a small dark or light object of any shape moved slowly through the receptive-field center or to turning a small stationary spot on or off. Large objects or diffuse light were usually much less effective. Less than one-quarter of superficial layer cells showed directional selectivity to a moving object, the majority of these favoring up and nasal movement. The chief visual cell type in the stratum opticum and upper part of the intermediate gray resembled in the newness neurons described for many other vertebrates: they had large receptive fields and responded best to up and nasal movement of a small dark or light object, whose optimal size was similar to the optimum for upper-layer cells. If the same part of the receptive field was repeatedly stimulated there was a marked tendency to habituate. Only very few cels responded to the ipsilateral eye. Intermixed with visual cells in the upper part of the intermediate gray were cells that responded to somatosensory or auditory stimuli. Here bimodal and trimodal cells were also seen. In deeper layers somatosensory and auditory modalities tended to take over. These two modalities were not segregated into sublayers but rather seemed to be arranged in clusters. Responses to somatosensory and auditory stimuli were brisk, showing little habituation to repeated stimulation.

Cortex-restricted disruption of NMDAR1 impairs neuronal patterns in the barrel cortex

Abstract: In the rodent primary somatosensory cortex, the configuration of whiskers and sinus hairs on the snout and of receptor-dense zones on the paws is topographically represented as discrete modules of layer IV granule cells (barrels) and thalamocortical afferent terminals. The role of neural activity, particularly activity mediated by NMDARs (N-methyl-D-aspartate receptors), in patterning of the somatosensory cortex has been a subject of debate. We have generated mice in which deletion of the NMDAR1 (NR1) gene is restricted to excitatory cortical neurons, and here we show that sensory periphery-related patterns develop normally in the brainstem and thalamic somatosensory relay stations of these mice. In the somatosensory cortex, thalamocortical afferents corresponding to large whiskers form patterns and display critical period plasticity, but their patterning is not as distinct as that seen in the cortex of normal mice. Other thalamocortical patterns corresponding to sinus hairs and digits are mostly absent. The cellular aggregates known as barrels and barrel boundaries do not develop even at sites where thalamocortical afferents cluster. Our findings indicate that cortical NMDARs are essential for the aggregation of layer IV cells into barrels and for development of the full complement of thalamocortical patterns.