Overlapping representation of fingers in the somatosensory cortex (area 2) of the conscious monkey

Finger representation on the first somatosensory cortex was mapped in conscious monkeys by single-unit recording. While representation was somatotopic in area 3, this was not the case in area 2, where the representation of different fingers overlapped. Our results indicate that area 2 is not a pure replica of the receptor sheet of the body surface.     

Cortical and thalamic connections of the parietal ventral somatosensory area in marmoset monkeys (Callithrix jacchus).

Microelectrode mapping methods were used to define the parietal ventral somatosensory area (PV) on the upper bank of the lateral sulcus in five marmosets (Callithrix jacchus). In the same animals, neuroanatomical tracers were placed into electrophysiologically identified sites in PV and/or the second somatosensory area (S2). Foci of anterograde and retrograde label were related to electrophysiological maps of cortical areas and cortical and thalamic architecture. The results lead to the following conclusions: (1) Multiunit recordings from cortex on the upper bank of the lateral sulcus demonstrate that PV is somatotopically organized, with the face representation adjoining area 3b and the hindlimb and tail representations away from this border in cortex deep on the upper bank of the lateral sulcus. The forelimb representation is caudal in PV adjacent to the S2 forelimb representation. The body surface representation in PV approximates a mirror image of that in S2; (2) Areas PV and S2 are less myelinated and have less cytochrome oxidase enzyme activity than area 3b; (3) The ventroposterior inferior nucleus (VPI) of the thalamus provides the major somatosensory projections to PV. PV is reciprocally connected with VPI and anterior pulvinar; (4) PV has ipsilateral cortical connections with areas 3a, 3b, 1, and M1 and higher order somatosensory fields, and at least most of these connections are somatotopically matched; and (5) Callosal connections of PV are with S2 and PV of the other cerebral hemisphere. These results further establish PV as one of at least four somatosensory areas of the lateral sulcus of primates.     

Adaptive changes in the neuromagnetic response of the primary and association somatosensory areas following repetitive tactile hand stimulation in humans

Cortical adaptation in the primary somatosensory cortex (SI) has been probed using different stimulation modalities and recording techniques, in both human and animal studies. In contrast, considerably less knowledge has been gained about the adaptation profiles in other areas of the cortical somatosensory network. Using magnetoencephalography (MEG), we examined the patterns of short‐term adaptation for evoked responses in SI and somatosensory association areas during tactile stimulation applied to the glabrous skin of the hand. Cutaneous stimuli were delivered as trains of serial pulses with a constant frequency of 2 Hz and 4 Hz in separate runs, and a constant inter‐train interval of 5 s. The unilateral stimuli elicited transient responses to the serial pulses in the train, with several response components that were separated by independent component analysis. Subsequent source reconstruction techniques identified regional generators in the contralateral SI and somatosensory association areas in the posterior parietal cortex (PPC). Activity in the bilateral secondary somatosensory cortex (i.e., SII/PV) was also identified, although less consistently across subjects. The dynamics of the evoked activity in each area and the frequency‐dependent adaptation effects were assessed from the changes in the relative amplitude of serial responses in each train. We show that the adaptation profiles in SI and PPC areas can be quantitatively characterized from neuromagnetic recordings using tactile stimulation, with the sensitivity to repetitive stimulation increasing from SI to PPC. A similar approach for SII/PV has proven less straightforward, potentially due to the tendency of these areas to respond selectively to certain stimuli. Hum Brain Mapp, 2013. © 2012 Wiley Perodicals, Inc.     

The effect of stimulation type,head modeling,and combined EEG and MEG on the source reconstruction of the somatosensory P20/N20 component

Modeling and experimental parameters influence the Electro‐ (EEG) and Magnetoencephalography (MEG) source analysis of the somatosensory P20/N20 component. In a sensitivity group study, we compare P20/N20 source analysis due to different stimulation type (Electric‐Wrist [EW], Braille‐Tactile [BT], or Pneumato‐Tactile [PT]), measurement modality (combined EEG/MEG – EMEG, EEG, or MEG) and head model (standard or individually skull‐conductivity calibrated including brain anisotropic conductivity). Considerable differences between pairs of stimulation types occurred (EW‐BT: 8.7 ± 3.3 mm/27.1° ± 16.4°, BT‐PT: 9 ± 5 mm/29.9° ± 17.3°, and EW‐PT: 9.8 ± 7.4 mm/15.9° ± 16.5° and 75% strength reduction of BT or PT when compared to EW) regardless of the head model used. EMEG has nearly no localization differences to MEG, but large ones to EEG (16.1 ± 4.9 mm), while source orientation differences are non‐negligible to both EEG (14° ± 3.7°) and MEG (12.5° ± 10.9°). Our calibration results show a considerable inter‐subject variability (3.1–14 mS/m) for skull conductivity. The comparison due to different head model show localization differences smaller for EMEG (EW: 3.4 ± 2.4 mm, BT: 3.7 ± 3.4 mm, and PT: 5.9 ± 6.8 mm) than for EEG (EW: 8.6 ± 8.3 mm, BT: 11.8 ± 6.2 mm, and PT: 10.5 ± 5.3 mm), while source orientation differences for EMEG (EW: 15.4° ± 6.3°, BT: 25.7° ± 15.2° and PT: 14° ± 11.5°) and EEG (EW: 14.6° ± 9.5°, BT: 16.3° ± 11.1° and PT: 12.9° ± 8.9°) are in the same range. Our results show that stimulation type, modality and head modeling all have a non‐negligible influence on the source reconstruction of the P20/N20 component. The complementary information of both modalities in EMEG can be exploited on the basis of detailed and individualized head models.     

Cortical connections of the second somatosensory area and the parietal ventral area in macaque monkeys

To gain insight into how cortical fields process somatic inputs and ultimately contribute to complex abilities such as tactile object perception, we examined the pattern of connections of two areas in the lateral sulcus of macaque monkeys: the second somatosensory area (S2), and the parietal ventral area (PV). Neuroanatomical tracers were injected into electrophysiologically and/or architectonically defined locations, and labeled cell bodies were identified in cortex ipsilateral and contralateral to the injection site. Transported tracer was related to architectonically defined boundaries so that the full complement of connections of S2 and PV could be appreciated. Our results indicate that S2 is densely interconnected with the primary somatosensory area (3b), PV, and area 7b of the ipsilateral hemisphere, and with S2, 7b, and 3b in the opposite hemisphere. PV is interconnected with areas 3b and 7b, with the parietal rostroventral area, premotor cortex, posterior parietal cortex, and with the medial auditory belt areas. Contralateral connections were restricted to PV in the opposite hemisphere. These data indicate that S2 and PV have unique and overlapping patterns of connections, and that they comprise part of a network that processes both cutaneous and proprioceptive inputs necessary for tactile discrimination and recognition. Although more data are needed, these patterns of interconnections of cortical fields and thalamic nuclei suggest that the somatosensory system may not be segregated into two separate streams of information processing, as has been hypothesized for the visual system. Rather, some fields may be involved in a variety of functions that require motor and sensory integration.     

Corticocortical projections to representations of the teeth,tongue, and face in somatosensory area 3b of macaques

We placed injections of anatomical tracers into representations of the tongue, teeth, and face in the primary somatosensory cortex (area 3b) of macaque monkeys. Our injections revealed strong projections to representations of the tongue and teeth from other parts of the oral cavity responsive region in 3b. The 3b face also provided input to the representations of the intraoral structures. The primary representation of the face showed a pattern of intrinsic connections similar to that of the mouth. The area 3b hand representation provided little to no input to either the mouth or the face representations. The mouth and face representations of area 3b received projections from the presumptive oral cavity and face regions of other somatosensory areas in the anterior parietal cortex and the lateral sulcus, including areas 3a, 1, 2, the second somatosensory area (S2), the parietal ventral area (PV), and cortex that may include the parietal rostral (PR) and ventral somatosensory (VS) areas. Additional inputs came from primary motor (M1) and ventral premotor (PMv) areas. This areal pattern of projections is similar to the well‐studied pattern revealed by tracer injections in regions of 3b representing the hand. The tongue representation appeared to be unique in area 3b in that it also received inputs from areas in the anterior upper bank of the lateral sulcus and anterior insula that may include the primary gustatory area (area G) and other cortical taste‐processing areas, as well as a region of lateral prefrontal cortex (LPFC) lining the principal sulcus. J. Comp. Neurol. 522:546–572, 2014. © 2013 Wiley Periodicals, Inc.     

Neural systems connecting interoceptive awareness and feelings

In many theories of emotions the representations of bodily responses play an important role for subjective feelings. We tested the hypothesis that the perception of bodily states is positively related to the experienced intensity of feelings as well as to the activity of first-order and second-order brain structures involved in the processing of feelings. Using a heartbeat perception task, subjects were separated into groups with either high or poor interoceptive awareness. During emotional picture presentation we measured high-density EEG and used spatiotemporal current density reconstruction to identify regions involved in both interoceptive awareness and emotion processing. We observed a positive relation between interoceptive awareness and the experienced intensity of emotions. Furthermore, the P300 amplitudes to pleasant and unpleasant pictures were enhanced for subjects with high interoceptive awareness. The source reconstruction revealed that interoceptive awareness is related to an enhanced activation in both first-order structures (insula, somatosensory cortices) and second-order structures (anterior cingulate, prefrontal cortices). We conclude that the perception of bodily states is a crucial determinant for the processing and the subjective experience of feelings.     

Sensorimotor training promotes functional recovery and somatosensory cortical map reactivation following cervical spinal cord injury

Sensorimotor activity has been shown to play a key role in functional recovery after partial spinal cord injury (SCI). Most studies in rodents have focused on the rehabilitation of hindlimb locomotor functions after thoracic or lumbar SCI, whereas forelimb motor and somatosensory abilities after cervical SCI remain largely uninvestigated, despite the high incidence of such injuries in humans. Moreover, little is known about the neurophysiological substrates of training‐induced recovery in supraspinal structures. This study was aimed at evaluating the effects of a training procedure combining both motor and sensory stimulation on behavioral performance and somatosensory cortical map remodeling after cervical (C4–C5) spinal hemisection in rats. This SCI severely impaired both sensory and motor capacities in the ipsilateral limbs. Without training, post‐lesion motor capacities gradually improved, whereas forepaw tactile abilities remained impaired. Consistently, no stimulus‐evoked responses were recorded within the forepaw representational zone in the primary somatosensory (S1) cortex at 2 months after the SCI. However, our data reveal that with training started from the 7th day post‐lesion, a nearly complete recovery (characterized by an early and rapid improvement of motor functions) was associated with a gradual compensation of tactile deficits. Furthermore, the recovery of tactile abilities was correlated with the areal extent of reactivation of S1 cortex forepaw representations. Rehabilitative training promoted post‐lesion adaptive plasticity, probably by enhancing endogenous activity within spared spinal and supraspinal circuits and pathways sustaining sensory and motor functions. This study highlights the beneficial effect of sensorimotor training in motor improvement and its critical influence on tactile recovery after SCI.     

Somatotopic organization of the lateral sulcus of owl monkeys: area 3b, S-II, and a ventral somatosensory area

Multiunit microelectrode recordings and injections of horseradish peroxidase (HRP) were used to reveal neuron response properties, somatotopic organization, and interconnections of somatosensory cortex in the lateral sulcus (sylvian fissure) of New World owl monkeys. There were a number of main findings. 1) Representations of the face and head in areas 3b, 1, and S-II are found on the upper bank of the lateral sulcus. Most of the mouth and lip representations of area 3b were found in a rostral extension along the lip of the lateral sulcus. Adjacent cortex deeper in the lateral sulcus represented the nose, eye, ear, and scalp. 2) S-II was located on the upper bank of the lateral sulcus and extended past the fundus onto the deepest part of the lower bank. The face was represented most superficially in the sulcus, with the hand, foot, and trunk located in a rostrocaudal sequence deeper in the sulcus. The orientation of S-II is "erect," with the limbs pointing away from area 3b. 3) Neurons in S-II were activated by light tactile stimulation of the contralateral body surface. Receptive fields were several times larger than for area 3b neurons. 4) A 1-2-mm strip of cortex separating the face and hand representations in S-II was consistently responsive to the stimulation of deep receptors but was unresponsive to light cutaneous stimulation. 5) Injections of horseradish peroxidase in the electrophysiologically identified hand or foot representations of area 3b revealed somatotopically matched interconnections with mapped hand and foot representations in S-II. 6) A systematic representation of the body, termed the "ventral somatic" area, VS, was found extending laterally from S-II on the lower bank of the lateral sulcus. Within VS, the hand and foot were represented deep in the sulcus along the hand and foot regions of S-II, and the face was lateral near the ventral lip of the sulcus. 7) Neurons at most recording sites in the VS region were activated by contralateral cutaneous stimuli. However, a few sites had neurons with bilateral receptive fields. Receptive field sizes were comparable to those in S-II. In addition, neurons in islands of cortex in the VS region had properties that suggested that they were activated by pacinian receptors, while other regions were difficult to activate by light tactile stimuli but responded to stimuli that would activate deep receptors. 8) A few recording sites caudal to S-II on the upper bank of the lateral sulcus were responsive to somatic stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cortical somatosensory and trigeminal inputs to the cat superior colliculus: Light and electron microscopic analyses

Two different axonal transport tracers were used in single animals to test the hypothesis that the expansive intermediate gray layer of the cat superior colliculus (stratum griseum intermediale, SGI) is composed of sensorimotor domains. The results show that two sensory pathways, the trigeminotectal and the corticotectal arising from the fourth somatosensory area, commingle in patches across the middle tier of the SGI. Furthermore, the data reveal that tectospinal cells are distributed within these patches. Taken together, these results show a commingling of functionally related afferents and a consistent spatial relationship between these afferents and tectospinal neurons. These relationships indicate that the SGI consists of domains that can be distinguished by their unique combinations of afferent and efferent connections. The ultrastructural characteristics and synaptic relationships of these somatosensory afferent pathways suggest that they have distinct roles within the sensorimotor domain of the SGI. The trigeminotectal terminals are relatively small, contain round vesicles and make asymmetrical synapses on small, presumably distal, dendrites. We submit that these trigeminal terminals bestow the basic receptive field properties upon SGI neurons. In contrast, the somatosensory corticotectal terminals are relatively large, contain round vesicles, make asymmetrical synapses, participate in triads, and are presynaptic to proximal dendrites. We suggest that these cortical terminals bestow integrative abilities on SGI neurons. J. Comp. Neurol. 388:313–326, 1997. © 1997 Wiley-Liss, Inc.     

Haptic contents of a movie dynamically engage the spectator's sensorimotor cortex

Observation of another person's actions and feelings activates brain areas that support similar functions in the observer, thereby facilitating inferences about the other's mental and bodily states. In real life, events eliciting this kind of vicarious brain activations are intermingled with other complex, ever‐changing stimuli in the environment. One practical approach to study the neural underpinnings of real‐life vicarious perception is to image brain activity during movie viewing. Here the goal was to find out how observed haptic events in a silent movie would affect the spectator's sensorimotor cortex. The functional state of the sensorimotor cortex was monitored by analyzing, in 16 healthy subjects, magnetoencephalographic (MEG) responses to tactile finger stimuli that were presented once per second throughout the session. Using canonical correlation analysis and spatial filtering, consistent single‐trial responses across subjects were uncovered, and their waveform changes throughout the movie were quantified. The long‐latency (85–175 ms) parts of the responses were modulated in concordance with the participants’ average moment‐by‐moment ratings of own engagement in the haptic content of the movie (correlation r = 0.49; ratings collected after the MEG session). The results, obtained by using novel signal‐analysis approaches, demonstrate that the functional state of the human sensorimotor cortex fluctuates in a fine‐grained manner even during passive observation of temporally varying haptic events. Hum Brain Mapp 37:4061–4068, 2016. © 2016 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.     

Topical application of morphine to the rat somatosensory cortex produces analgesia to tonic pain

Topical application of 0.01 or 0.1% morphine solution to the somatosensory SI area of the rat cerebral cortex significantly decreased the pain intensity rating in the formalin test without producing motor side effects or sensory deficits. Naloxone partially antagonizes this effect. Topical application of morphine to the striate cortex did not induce analgesia. It is suggested that the primary somatosensory SI area of the cerebral cortex plays a role in opiate pain control.     

Functional connectivity between forearm and digits representations in human somatosensory area 3b.

OBJECTIVE: We compared the effects of tactile interference to the forearm on magnetic responses evoked by electric stimulation of the little finger (D5) and the thumb (D1). METHODS: Electric stimulation was delivered to D5 or D1 individually. In each stimulus session, magnetic recordings were conducted with or without concurrent tactile interference to the radial side of the anterior forearm. RESULTS: With forearm interference, the amplitude of the primary response (N20m) following D5 stimulation was reduced to 90.7% of the control value without interference, while that following D1 stimulation was not affected (100.7%). CONCLUSIONS: In human somatosensory area 3b, the representation of the forearm is immediately adjacent to that of the D5, and distant from that of the D1. Thus, the result suggests that the tactile interference effect on N20m depends on the cortical distance between electrically and mechanically activated 3b areas. SIGNIFICANCE: Intrinsic synaptic connections between the 3b hand representation and its surroundings have been hypothesized as a neural basis for plastic changes of the human brain, such as a phantom hand phenomenon. The present finding implies that these connections may play some physiological roles even in normal adult humans.     

Cortical connections of the somatosensory fields of the lateral sulcus of macaques: evidence for a corticolimbic pathway for touch

The ipsilateral corticocortical connections of the somatosensory fields of the lateral sulcus of macaques were examined with both anterograde and retrograde axonal transport methods. In most cases, the field of interest was identified prior to the injection of the tracer substance by recording neuronal responses to somatic stimulation. The results show that the second somatosensory area (S2) is reciprocally connected with the retroinsular area (Ri), area 7b, and the granular (Ig) and dysgranular (Id) insular fields. Ri is also reciprocally connected with Ig. Previously reported connections were confirmed between S2 and areas 3a, 3b, 1, and 2 and between area 5 and both area 7 and Ri. Moreover, the portions of Ig and Id that receive somatic inputs were shown to project to the amygdaloid complex. Id projects, in addition, to the perirhinal cortex, which supplies input to the hippocampal formation. The corticocortical projections were found to have two distinct laminar patterns of termination. One is characterized by heavy terminations in layers IV and IIIb and the other by heavy terminations in layer I, but no terminations in layers IV and IIIb. These two patterns were typically found to be reciprocally related. The results suggest that somatosensory information is processed by a series of cortical fields, including areas 3a, 3b, 1, 2, 5, 7b, S2, Ig, and Id. These fields have access to the amygdaloid complex and the hippocampal formation. Thus, a ventrally directed tactile processing pathway can be followed from S1 to the temporal lobe limbic structures via relays in S2 and the insula; this corticolimbic pathway may subserve tactile learning and memory.     

Topography and architecture of visual and somatosensory areas of the agouti

We analyzed the organization of the somatosensory and visual cortices of the agouti, a diurnal rodent with a relatively big brain, using a combination of multiunit microelectrode recordings and histological techniques including myelin and cytochrome oxidase staining. We found multiple representations of the sensory periphery in the parietal, temporal, and occipital lobes. While the agouti's primary (V1) and secondary visual areas seemed to lack any obvious modular arrangement, such as blobs or stripes, which are found in some primates and carnivores, the primary somatosensory area (S1) was internally subdivided in discrete regions, isomorphically associated with peripheral structures. Our results confirm and extend previous reports on this species, and provide additional data to understand how variations in lifestyle can influence brain organization in rodents. J. Comp. Neurol. 522:2576–2593, 2014. © 2014 Wiley Periodicals, Inc.     

Mechanical vibratory stimulation of feline forepaw skin induces long-lasting potentiation in the secondary somatosensory cortex

We investigated the long-lasting effects of mechanical vibratory stimulation of the skin on the excitability of feline cortical neurons in the forelimb areas of the primary (SI) and secondary (SII) somatosensory cortices. Conditioning mechanical stimuli were 300 bursts of 10 pulses at 200 Hz delivered with a 10-s interburst interval from a mechanical stimulator. Test field potentials and unit discharges were evoked by electrical stimulation to the ventral posterolateral thalamic nucleus (VPL) or by single mechanical stimuli applied to the skin. In SII, the mechanical burst stimulation to the skin increased the amplitudes of field potentials and the frequency of unit discharges elicited by single mechanical stimuli applied to the skin. The vibratory conditioning stimulus also produced a similar potentiation of the VPL-evoked field potentials (126-139% increase in amplitude, P < 0.05) with an associated increase in firing rates of extracellularly recorded neuronal activity (117%, P < 0.001). These potentiations persisted through the entire experimental period of 120 min. The translaminar current source density analysis calculated from the VPL-evoked field potentials increased to 127% of the control value (P < 0.01). In contrast, in SI we observed no significant changes in the field potential amplitudes or in the currents generated in superficial layers (91-117%). Taken together with the previous finding that tetanic electrical stimulation of VPL induces long-lasting potentiation of the VPL-evoked cortical responses in SII but not of those in SI, the present results suggest that SII has a large capacity for the rapid functional plasticity involved in the learning that occurs during repeated tactile experiences.     

Cortical responses to self and others

The extrastriate body area (EBA) is one among the multiple, functionally specialized regions of the human visual cortex exhibiting modulation by body-related stimuli. Here we investigate whether activation patterns differ for the perception of one's own body and the bodies of others. We used functional magnetic resonance imaging to identify body-related brain areas and to see how these areas differentiate between images of one's own body and those of others in the absence of facial or motion cues. Whole brain explorative group-level analysis identified body-related blood oxygen level dependent (BOLD) signal enhancement in five regions of the right and in one region of the left hemisphere (right: in the extrastriate visual and parietal cortex and in the precentral gyrus, left: in the extrastriate visual cortex). General linear model group-level random effects analysis of the self-other contrast revealed self-related responses in the extrastriate and parietal regions in the right hemisphere but also in the right middle frontal gyrus. These results suggest the existence of a cortical network for the extraction of body-related information and another cortical network for the extraction of self-related body information. The two networks partially overlap in the right superior and inferior parietal cortices, but are clearly segregated in the extrastriate visual cortex and in the middle frontal gyrus. In addition, we report that the classical EBA is only involved in the analysis of body-related information but not in the assignment of body identity. The latter appears to be accomplished by a network in right hemisphere comprising the fusiform body area, regions of the superior parietal lobe, the inferior parietal cortex, and the middle frontal gyrus.     

Receptive fields of neurons in areas 3b and 1 of somatosensory cortex in monkeys

Receptive fields of neurons within the separate representations of the glabrous hand in areas 3b and 1 of somatosensory cortex were studied in cynomolgus monkeys. Many neurons in area 1 have center-surround receptive fields with separate 'on' and 'off' zones, while neurons in area 3b exhibit largely uniform or homogeneous receptive fields.     

Long-lasting potentiation of field potentials in primary and secondary somatosensory cortex

Effects of tetanic bursts (200 Hz, 10 pulses) on field potentials elicited by ventral posterolateral thalamic nucleus (VPL) stimulation were investigated in the feline somatosensory cortex. In the first experiments, field potentials elicited by VPL stimulation (test pulse) were simultaneously recorded in the primary (SI) and the secondary (SII) somatosensory cortex in six animals. Potentiation of field potentials recorded in SII was induced by tetanic stimulation of VPL in all six animals, whereas the same tetanic bursts failed to produce significant changes in SI in four of the six animals. The results suggest that plastic changes in somatosensory processing take place in SII rather than SI. In subsequent experiments, features of the potentiation observed in SII were examined in 20 animals. The field potentials were simultaneously recorded at 16 points placed vertically at 150-μm intervals from the cortical surface. The potentiation of field potentials (to 110–170% of control values) observed at depths between 600 and 1350 μm lasted more than 90 min after tetanic stimulation. Poststimulus histograms of multiple-unit activities revealed a long-lasting increase in the number of unit discharges evoked by VPL stimulation. This change in the number of activated cellsis regarded as a cause of potentiation of SII field potentials. In the last session, the effects of N-methyl-d-aspartate (NMDA) receptor antagonists on the potentiation of SII field potentials were investigated. Cortical intraventricular injection ofd-2-amino-5-phosphonovalerate (APV) anddl-2-amino-7-phosphonoheptanoic acid (APH) prevented induction of the potentiation in SII. NMDA receptor activation participates in forming this SII potentiation.     

Correlating cytoarchitecture and function in cat primary somatosensory cortex: the challenge of individual differences

Principles of organization for the primary somatosensory cortex are generalizations derived by examining data obtained in different individuals. The manner in which these data are combined influences the conclusions derived. We found the line representing the widest anteroposterior distance across the sigmoid gyrus to be a useful reference in the cat somatosensory cortex for combining and comparing electrophysiological and cytoarchitectonic data from different individuals when we constructed cytoarchitectonic and functional maps of the bank of the medial ansate sulcus; maps prepared from combined data sets had boundaries similar to those found among individuals. Nevertheless, we argue that, for reasons inherent to the nature of the cerebral hemispheres and cortical maps, such references will never allow combinations of data capable of defining a unique high resolution prototypical map of individual body parts; the somatotopic order of body representations is, as are certain other attributes of somatosensory cortex, idiosyncratic. The genetic, developmental and use-dependent reasons for this situation are discussed.