Which Cortex Registers And Processes By Touch

Organization of the Nervous System I

Wanda Thousand. Webb PhD, CCC-SLP , in Neurology for the Spoken communication-Language Pathologist (6th Edition), 2017

Principal Somatosensory Cortex

The main somatosensory cortex (areas 1, 2, and 3) is on the postcentral gyrus and is a primary receptor of general bodily awareness. Thalamic radiations relay sensory data from skin, muscles, tendons, and joints of the body to the master somatosensory cortex. Lesions of this cortex produce partial sensory loss (paresthesia); rarely does complete sensory loss (anesthesia) occur . A lesion causes numbness and tingling in the opposite side of the trunk. Widespread destructive lesions produce gross sensory loss with an inability to localize sensation.

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Anatomy and Physiology, Systems

J.H. Kaas , in Encephalon Mapping, 2015

Receptors and Peripheral Nerve Afferents

Primary somatosensory cortex (S1) is activated by touch and pressure level on the glabrous pare and the motility of hairs on the hairy skin. Almost all mammals have specialized receptors ( Abraira & Ginty, 2013) around the base of the long whiskers or vibrissae that are used to find objects at a short distance from the body. These long vibrissae are usually nigh densely distributed on the side of the confront and lower jaw, but they also occur above the heart, on the wrist, and on other locations on the torso (Brecht, Preilowski, & Merzenich, 1997). Such sensory vibrissae are variable in number and location across species, but they have received the nigh attention in rats and mice as the long mystacial vibrissae are individually represented in S1, likewise as in the ventroposterior (VP) nucleus and trigeminal nuclei of the brain stem. In S1, the collection of neurons best activated by a single whisker is visible in several different stains of brain sections. This collection of neurons for an private whisker has been given the colorful name the 'cortical barrel.' The function of S1 with rows of 'barrels' corresponding to rows of whiskers is called the 'barrel field.' These mystacial whiskers observe and help identify objects near the face up and mouth. Shorter hairs on the upper and lower jaws are more finely spaced and they provide more details near objects that may be identified as food (Brecht et al., 1997).

Other peripheral nerve afferents subserving touch are associated with morphologically specialized receptor cells in the pare. These specialized receptors allow afferent types to lawmaking different features of touch and provide different types of data to the brain (Abraira & Ginty, 2013). The Merkel cells mediate the responses of the slowly adapting blazon 1 afferents (SA-I) that bespeak a maintained affect the peel or displacement of a pilus. Type two slowly adapting afferents (SA-II) point pare deformations, pressure level on teeth, and tendon stretch during move. Type I rapidly adapting afferents (RA-I), from receptors in hair follicles and skin, signal changes in skin contact and surface texture. The highly specialized Pacinian corpuscles for quickly adapting blazon Ii afferents (SA-II) are deeper in the peel and are very sensitive to vibration. SA-Two afferents might, for case, detect the vibrations that travel through the ground that are fabricated by an approaching predator. Other afferents signal tissue harm (hurting), temperature, and poorly localized impact.

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Somatosensory Organisation

Ford F. Ebner , Jon H. Kaas , in The Rat Nervous Arrangement (4th Edition), 2015

Motor Cortex

Main somatosensory cortex provides a major activating input to motor cortex in rats. In rats, the primary motor surface area, M1, has been the most studied, and microstimulation studies have demonstrated that M1 contains a systematic representation of body part movements, from hindlimb to confront, in a mediolateral sequence beyond cortex, forming a somatotopic representation that parallels that plant in S1, but less somatotopically ordered ( Donoghue and Wise, 1982; Sanderson et al., 1984; Neafsey et al., 1986). As movements tin can be evoked from dysgranular S1 and even from parts of granular S1, especially the hindlimb portion, some investigators have proposed a fractional overlap of part of S1 with function of M1 (Sanderson et al., 1984). Corticospinal projections originate from both M1 and S1, including hindlimb and forelimb portions, while barrel field regions projection to the brainstem (Wise et al., 1979; Li et al., 1990). The S1 projections originate from both S1 proper (granular S1) and dysgranular S1. Corticospinal projections from S1 may reverberate motor functions, but their terminations in the contralateral dorsal horn of the spinal grayness affair advise a more sensorimotor part (Li et al., 1990). There is also a ventral ipsilateral component of the corticospinal project (Brösamle and Schwab, 1997). Because of the sensorimotor or motor functions of S1 proper and dysgranular S1, it is not necessary to conclude that M1 partially overlaps S1. Instead, M1 in agranular cortex is a complete representation, including the hindlimb, and this complete representation is more than specifically involved in motor functions (Li et al., 1990). M1 projects to the lower brainstem and spinal cord in a somatotopic blueprint that reflects the motor functions of levels of the brainstem and spinal cord (Miller, 1987; Li et al., 1990).

Finally, in that location is evidence for a less well understood and variously named second motor area, M2, best known for a second representation of forelimb movements, and referred to as the rostral forelimb area (RFA). However, evidence has accumulated for the conclusion that this more than rostral motor area has a consummate representation of torso movements (Neafsey and Sievert, 1982; Tandon et al., 2008; Mohammed and Jain, 2013). M1 projects to the rostral motor area, M2, and receives sparser projections back from M2. This second motor area also projects to the brainstem and spinal string, simply much more sparsely (Wise et al., 1979; Li et al., 1990). Additionally, a few neurons in the S2 and PV regions project to the spinal cord. Motor cortex gets most of its thalamic inputs from the motor thalamus, merely a few neurons from the VP complex may also contribute.

The projections from S1 to M1 originate primarily from the septal regions rather than the modules with densely packed layer 4 cells, the barrels and barrel-like structures (Kim and Ebner, 1999; Alloway et al., 2004; Chakrabarti and Alloway, 2006). Other projections to M1 are from dysgranular cortex (Donoghue and Parham, 1983; Kim and Lee, 2013). The projections from the S1 butt field to M1 are organized to facilitate the integration of information from the same row of whiskers (Hoover et al., 2003). Some neurons that project to M1 also projection to S2. As the inputs to M1 are primarily from septa, the septal regions of S1 appear to exist most involved in guiding motor behavior. M1 likewise has reciprocal connections with S2 and probably PV, the basal ganglia, the thalamus, the superior colliculus, the inductive pretectal nucleus and the brainstem and spinal cord (Li et al., 1990; Miyashita et al., 1994). Other cortical connections of M1 include the region of M2.

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Cutaneous Sensory Systems

Joseph Feher , in Quantitative Man Physiology (Second Edition), 2012

The Cutaneous Senses Map onto the Sensory Cortex

The chief somatosensory cortex is called S1. This area of the cerebral cortex receives sensory information from the somatic senses, plus proprioceptive senses and some visceral senses. It is located on the postcentral gyrus of the parietal lobe, equally shown in Figure 4.3.vi. The topological arrangement of the somatic senses is preserved equally they enter the spinal cord, travel upwardly the dorsal column tracts, to the nucleus gracilis or nucleus cuneatus, and is preserved through the thalamus to somewhen map onto the cortex. Thus the surface of the body maps onto the surface of the brain.

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Hurting

R.D. Treede , A.V. Apkarian , in The Senses: A Comprehensive Reference, 2008

v.45.three.1 The Primary Somatosensory Cortex

The primary somatosensory cortex (SI) is located in the anterior office of the parietal lobe, where information technology constitutes the postcentral gyrus. It consists of Brodmann areas one, two, 3a, and 3b ( Figure ii(a)). Areas 3b and 1 receive cutaneous tactile input, areas 3a and two proprioceptive input.

Nociceptive input to monkey SI was demonstrated anatomically. SI receives direct spino-thalamocortical input from the ventrobasal nuclei, in particular the ventro-posterolateral (VPL) nucleus (Gingold, South. I. et al., 1991). Nociceptive neurons in SI are found in clusters, raising the possibility that SI may incorporate nociceptive specific columns (Lamour, Y. et al., 1983). Since testify for nociceptive neurons in the most superficial cortical layers is lacking, this hypothesis has non yet been confirmed. Nociceptive neurons are rare in monkey SI and have mainly been establish in expanse i (Kenshalo, D. R. et al., 2000), whereas optical imaging techniques have also suggested nociceptive input to surface area 3a (Tommerdahl, Chiliad. et al., 1996). Thus, nociceptive signal processing within SI may exist spatially singled-out from tactile signal processing that is primarily directed to area 3b. There is as well some EEG and Million evidence in humans that nociceptive areas may exist situated more medially within SI than tactile areas with the same receptive fields, suggesting that nociceptive and tactile signal processing may occur in dissimilar subareas of SI (Ploner, Chiliad. et al. 2000; Schlereth, T. et al., 2003). Nociceptive input to homo SI has been confirmed by subdural recordings (Kanda, M. et al., 2000; Ohara, Due south. et al., 2004). Well-nigh 75% of the PET and fMRI studies reported activation of SI (Bushnell, Yard. C. et al., 1999; Apkarian, A. V. et al., 2005).

Nociceptive neurons in SI have small receptive fields (Effigy 2(b)) that are somatotopically bundled, and hence are ideally suited to code for the location of nociceptive stimuli (Kenshalo, D. R. and Isensee, O., 1983). Somatotopy of nociceptive processing in the human SI has been confirmed by EEG and PET studies (Tarkka, I. Yard. and Treede, R. D., 1993; Andersson, J. 50. R. et al., 1997). Activeness potential discharges of nociceptive SI neurons in monkey are modulated by the intensity of both mechanical and heat stimuli (Figures ii(c) and 2(d)) and their discharges correlate with detection speed (Kenshalo, D. R. et al., 1988). These findings suggest that nociceptive SI neurons are involved in the coding of pain intensity. This conclusion has been confirmed by a PET study of hypnotic modulation of perceived pain intensity that also modulated perfusion of SI (Hofbauer, R. K. et al., 2001) and by correlation analysis (Timmermann, L. et al., 2001).

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Somatosensation

R.Southward. Erzurumlu , in The Senses: A Comprehensive Reference, 2008

6.09.3.two Arrival of Thalamocortical and Other Afferents to the Somatosensory Cortex

The primary somatosensory cortex receives inputs from a variety of sources, such as the somatosensory thalamus (glutamatergic inputs), serotonergic projections from the midbrain raphé nuclei, noradrenergic projections from locus coeruleus ( D'Amato, R. J. et al., 1987; Bennett-Clarke, C. A. et al., 1991; Simpson, K. L., et al., 2006). Afferents from the dorsal thalamus, as well as raphé cortical projections, bear witness patterning in the barrel cortex. Noradrenergic inputs are not patterned according to cytoarchitectural landmarks.

Immunohistochemical localization of serotonin (v-HT) combined with autoradiographic imaging of serotonin-uptake sites in the neonatal rat somatosensory cortex showed a transient, dense, serotonergic innervation with dense patches over the cortical barrels (D'Amato, R.J. et al., 1987).

After studies confirmed the origin of these last patches from the raphé nuclei and raised the possibility that serotonergic inputs may assist TCAs in barrel-specific patterning. A dual labeling study with lipophilic tracers in fixed embryonic brains showed that thalamic afferents arrive in the somatosensory cortex well ahead of those projections from the raphé nuclei (Erzurumlu, R. S. and Jhaveri, S., 1992). Thus, it became credible that TCAs are the offset corticopetal projections to arrive in the somatosensory cortex and confer periphery-related patterns (Erzurumlu, R. S. and Jhaveri, Southward., 1990, 1992). Double labeling experiments further demonstrated that the patterning of TCAs in the rodent somatosensory cortex precedes other afferent terminals and extracellular matrix patterning seen in the developing barrel cortex (Bluish, One thousand. E. et al., 1991; Jhaveri, South. et al., 1991).

In mice, TCAs reach the somatosensory cortex later on embryonic day fifteen, and brainstorm probing the developing cortical plate by E18. Topographically organized TCAs invade the cortical plate by nascency (gestation xix days), as simple axons with very few branches (Senft, S. L. and Woolsey, T. A., 1991; Rebsam, A. et al., 2002; Lee, L. J., et al., 2005). Two days later, focalized terminal branches can exist seen in layer 4 and to a lesser extent in layer Six. Very few branches are seen in other layers. Developing TCAs can be visualized en masse by immunostaining for markers such as serotonin transporter. This approach allows for detection of emergence of the entire body map from a diffuse projection to segmentation of it into hindpaw and forepaw (lemniscal afferents) representation zones, lower lip and mystacial vibrissae representation zones (the posteromedial barrel subfield, and the representation area of the inductive snout with small sinus hairs. Once the body map is partitioned into these subterritories on postnatal twenty-four hour period two, further patterning into whisker-related rows (postnatal mean solar day three), and between postnatal days 35 sensory periphery-related patterning, that is, patchy distribution of TCAs sally (Rebsam, A. et al, 2002; Rebsam, A. and Gaspar, P., 2006) (Figure 3). Every bit barreloids (whisker- and digit-specific neural modules) develop in the thalamus, TCA terminal fields and arbors in the cortex segmentation into Gaussian patches (Senft, Due south. 50. and Woolsey, T. A., 1991), earlier the barrels appear every bit cellular modules (Figure 3). From postnatal mean solar day five onwards, selective pruning of overshooting collaterals, addition of more branches within focalized fields have place and TCAs consolidate their focal last arbors in layer IV with fewer terminal arbors in layer Half-dozen. Bifurcation points of axon arbors and terminal tips are mostly distributed in layer IV (about 75–80% of the total number), with some in layer VI (ten–15%) (Lee, L. J. et al., 2005).

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The Parietal Lobe

Samuel Harding-Forrester , Daniel E. Feldman , in Handbook of Clinical Neurology, 2018

Overview of rodent somatotopic maps

The primary somatosensory cortex (S1) of rats and mice – similar its primate homolog, area 3b – contains a somatotopic map of the contralateral trunk and face ( Figs four.3A–C, G). Rodent maps practise not contain major discontinuities as in primates: the caudorostral torso axis is mapped from medial to lateral in S1, with the limb representations extending anteriorly from the body and the confront representation continuous with the neck and body (Welker, 1976; Chapin and Lin, 1984), and the lower incisor and tongue lateral to the lower and upper jaws, respectively (Remple et al., 2003). The genitals are mapped in their somatotopically appropriate location betwixt the hindlimb and body (Lenschow et al., 2016). The forepaw and hindpaw representations are highly magnified, occupying 15% and 4% of the full map in rats, versus merely 14% devoted to the trunk, limbs, and tail (Dawson and Killackey, 1987).

The somatotopic map can be visualized histologically in L4 by staining for markers of thalamocortical axon terminals, or for mitochondrial enzymes enriched in highly active neurons, such as cytochrome oxidase (CO) (Fig. 4.3G). These stains reveal distinct cytochrome oxidase-rich anatomic modules in L4, which correspond the individual pads and digits of each paw (Waters et al., 1995) and the individual whiskers (vibrissae) within the facial map (Woolsey and Van der Loos, 1970). The whisker modules are known as "barrels" due to their ovoid shape. Rodent whiskers include small tactile hairs on the upper and lower lips (microvibrissae) that passively sense object features, and larger tactile hairs on each side of the face (macrovibrissae) that are actively moved, using specialized muscles, to detect and palpate objects ("whisking"; Brecht et al., 1997; reviewed in Diamond et al., 2008). In the rat, representations of the upper-lip and lower-lip microvibrissae account for 25% and ix% of the unabridged S1 map, respectively, while the macrovibrissae representation occupies 34% (Dawson and Killackey, 1987). This extreme magnification also occurs in mice and several other muridae, and reflects the behavioral salience of the whiskers as local object detectors (Woolsey et al., 1975; reviewed in Krubitzer et al., 2011).

The whisker barrels have been extensively studied. Rat and mouse macrovibrissae (henceforth, "whiskers") are organized on the confront into five rows (denoted A–E) and four or more arcs (denoted by numbers; thus, A1–A4; B1–B5, etc.) (Fig. four.3A). Each whisker is represented past a barrel in contralateral L4, with the barrels arranged isomorphically with the whiskers on the face, forming a precise topographic map (Fig. iv.3C). Each L4 barrel is a cluster of neurons that receives thalamocortical axonal input predominantly representing the corresponding whisker, and forms the center of a radial S1 column that processes this input (Fig. 4.3D). L4 barrels are closely apposed in mice, but in rats are separated by septal regions with lower cell density (Land and Simons, 1985). Thus, the S1 whisker map exhibits a clear modular columnar construction, with an orderly somatotopy axiomatic in the system of barrel columns. These features brand the whisker map a powerful model system for studying tactile representation, circuits, processing, and plasticity in cognitive cortex (reviewed in Feldmeyer et al., 2013). In rats, cytochrome oxidase staining oftentimes shows 2 to 3 subdomains within each barrel (Land and Erickson, 2005). These may correspond to singled-out termination zones of VPM axons (Furuta et al., 2011), but the functional correlates of these domains remain unknown.

S1 projects intracortically to ii next somatosensory areas, the secondary somatosensory cortex (S2) and the parietal ventral area (PV) (Fabri and Burton, 1991; Remple et al., 2003; Benison et al., 2007), both homologous to the synonymous regions in primates (Qi et al., 2008) (Fig. 4.iiiC). S2 lacks separate columns for each whisker, instead containing striplike domains each comprising a continuous representation of the whiskers of one row (eastward.g., A1–A4) in caudorostral order. These strips are arrayed isomorphically with the whisker rows on the confront, and the mediolateral lodge of the strips is a mirror reversal of the whisker rows in S1 (Hoffer et al., 2003). PV lacks detailed facial and whisker representations, but contains a body map mirroring that in S2. Thus, integrative processing through successive, mirrored representations is seen in rodent somatosensory cortex, every bit in primates.

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Memory Systems

N.M. Weinberger , in Learning and Retention: A Comprehensive Reference, 2008

3.11.6.three Primary Visual Cortex (V1)

In contrast to the main auditory and somatosensory cortices, there appear to be no studies of the specificity of associative processes in the main visual cortex. This is curious in light of the previous all-encompassing investigation of V1 in classical and instrumental conditioning in animals during the flow of 1935–1984. Equally noted earlier, most subsequent studies of V1 take focused on perceptual learning. Recent reports of classical workout in humans may indicate a resurrection of interest in associative learning. Functional magnetic resonance imaging (fMRI) has been used to investigate Pavlovian delay fear conditioning, using a blinking red light every bit the CS and shock equally the US (Knight et al., 1999). Paired subjects exhibited a larger amount of active tissue in V1 compared to controls that received light and shock unpaired. Yet, the individual group effects were a decrease in response in the controls and no change in the paired grouping, suggesting that associative processes prevented habituation in this case. The absence of a behavioral mensurate of learning limits interpretations also.

A further study of both delay and trace (ten due south) workout has been more revealing. Using a bigotry protocol in which the iii conditioned stimuli (CS+, CS+ trace, and CS−) were different colored shapes, the authors found significant behavioral learning and discrimination (development of conditioned galvanic peel responses, GSR) for both delay and trace protocols. Functional MRI responses were larger to the CS+ versus CS− in filibuster conditioning and also larger to the CS+ trace versus the CS− in trace conditioning.

Perhaps like studies volition be conducted in animals using a stimulus dimension (due east.g., line tilt) that could determine receptive field plasticity and thus reveal the extent of specificity of associative processes in V1. Given the earlier EEG and evoked potential studies, as well as the contempo fMRI experiments, there is reason to expect that, similar A1 and S1, V1 is specifically involved in associative learning and memory.

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Cortico-Basal Ganglia Networks and the Neural Substrates of Actions

Henry H. Yin , in Neurobiology of Alcohol Dependence, 2014

Sensorimotor Network and the Motor Hierarchy

The corticostriatal projections from primary motor and somatosensory cortices mainly send college-society kinesthetic and somesthetic signals (McGeorge & Faull, 1987, 1989). The sensorimotor network is where the labile motivational hierarchy and the fixed motor bureaucracy converge. The motor bureaucracy itself consists of at least four levels: muscle tension or force, muscle length, body configuration, and movement velocity (rate of change in body configuration). The lowest level of the hierarchy is the 1 controlling musculus tension, the final mutual path from motor neurons to muscle fibers. Immediately in a higher place this level there is muscle-length control (Merton, 1953; Powers, 1973). The third level of the motor hierarchy, control of trunk configuration, is situated in the brain stem postural control systems. The highest level in the intrinsic motor hierarchy is the command of movement velocity and serial order, which is hypothesized to be in the sensorimotor cortico-basal ganglia network.

Movement-velocity command is simply one case of a full general class of functions, all having to do with the control of the rate of change in different input variables. For proprioception, at this level in that location is the control of the charge per unit of change in body configurations; for other types of representations, the command of transitions in perceptions is no longer a part of the motor hierarchy. For example, the motion of some object in the visual field can be controlled by activity. This type of control characterizes what are normally chosen voluntary actions.

In the cerebral cortex, signals from multiple modalities can be combined to form abstract and invariant representations of proprioceptive, exteroceptive, and interoceptive stimuli (Cools, 1985; Konorski, 1967). The transition and rate of change in these representations can be controlled using negative feedback at the fourth level of the hierarchy. The basal ganglia, as a whole, announced to be disquisitional for control at the level of transition, regardless of the blazon of perceptual variables. Immediately beneath, the diencephalon and brainstem contain command systems for the command of body configurations.

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Barrel Cortex Circuits☆

Carl CH Petersen , in Reference Module in Biomedical Sciences, 2017

From Whisker to Cortex

While examining layer four of the rodent primary somatosensory cortex, Thomas Woolsey and Hendrik van der Loos discovered in 1970 that in that location are obvious cytoarchitectonic 'barrels' arranged identically to the whiskers on the snout ( Fig. 1(A) ). This remarkable mapping has inspired many neuroscientists to turn their attention to the signaling pathway from whisker to cortex. Indeed, the entire sensory pathway is remarkably well-delineated through stereotypical anatomical structures. The whiskers on the snout are laid out in a genetically-adamant blueprint and the large posterior mystacial whiskers have been given a nomenclature such that all researchers can hands identify, for case, the C2 whisker ( Fig. i(A) ). These large posterior whiskers are actively moved at high frequencies (~ 10 Hz) during 'whisking' when a rodent is exploring its environment. This active motion of the whiskers is idea to enhance sensitivity and discrimination abilities of this sensory signaling pathway in the same way that humans would move their fingertips beyond a surface in order to gather textural information.

A whisker contact with an object during whisking or a passive deflection of a whisker evokes activity in trigeminal ganglion neurons. These sensory neurons innervate the whisker follicle and presumably express mechanogated ion channels, which have not yet been identified at a molecular level. Deflection of a whisker volition induce mechanogated ionic currents, leading to action potential firing in the sensory trigeminal neurons. The sensory neurons respond to deflection of one and just i whisker, are highly selective to the direction of whisker deflection, and can be classified as rapidly adapting (RA) or slowly adapting (SA). Unlike trigeminal sensory neurons might encode distinct aspects of tactile awareness, some for example beingness activated past object contact and others by whisking in free air. Quantitative assay shows that the activity in the trigeminal ganglion neurons is extremely precise and highly reproducible, showing footling trial-to-trial variability.

These action potentials in the trigeminal ganglion neurons accurately encoding whisker sensation propagate to the brain stem, where they synaptically release glutamate onto brain stem neurons. The most important brain stem nucleus for processing of whisker information is the principal trigeminal (PrV) nucleus, which projects strongly to the ventral posterior medial (VPM) thalamus. The spinal trigeminal (SpV) complex of the brain stalk also receives whisker inputs and these neurons project to the posterior medial (POM) thalamus, to the ventrolateral aspect of the ventral posterior medial (VPMvl) thalamus, and to the tectum, zona incerta, and other encephalon regions. Both the PrV nucleus and some of the SpV nuclei contain articulate anatomical patterns termed 'barrelettes,' which are organized somatotopically. Many neurons in the PrV nucleus process predominantly single whisker information, whereas the SpV nuclei procedure predominantly multiwhisker information.

The thalamic VPM and POM regions both receive excitatory glutamatergic input from the brain stem relating to whisker sensation. The VPM thalamus, but not the POM thalamus, possesses somatotopically arranged 'barreloids.' Each barreloid processes sensory data primarily related to a unmarried whisker. Within a barreloid there is a map of direction tuning such that more dorsal neurons reply better to frontward and upwards whisker deflection direction. The neurons in the VPM thalamus generally respond with short latency and high precision to a single whisker, in agreement with a key office of this thalamic nucleus in relaying reliable sensory information to the cortex. Much less is known nigh the POM thalamus, but under anesthesia information technology appears to be largely inhibited through inputs from the zona incerta and, consistent with POM beingness a "higher guild" thalamic nucleus, information technology appears to exist strongly regulated past cortical input. Interestingly, in addition to innervating primary somatosensory cortex, POM also innervates secondary somatosensory cortex and whisker motor cortex. The physiological role of whisker information flowing through the POM region remains to be discovered.

The barreloid neurons of the VPM thalamus provide the major feed-forrad glutamatergic excitation to the master somatosensory barrel cortex. The chief target of innervation of the axons from a single barreloid is a barrel ( Fig. 1(B) ). The barrels are laid out somatotopically in neocortical layer four. The VPM neurons also projection weakly to a region spanning lower layer 5B and upper layer half dozen of the primary somatosensory cortex. The POM neurons provide a complementary glutamatergic innervation of the primary somatosensory cortex, with picayune input to the layer 4 barrels, but with dense innervation of layer ane and layer 5A, with some innervation of the layer 4 septal regions separating neighboring barrels. In contrast to the reliable encoding of sensory information at the periphery in the blueprint of activeness potential firing of the trigeminal ganglion neurons, responses in the neocortex are highly variable, maybe resulting from more complex context-dependent integration of sensorimotor activity with internal brain computations.

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