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Biomedical subjects

B L Whitsel

Publications and source records attributed to B L Whitsel.

At least 37 records · Page 2Linked to original sources
PubMed1989

Effects of traverse length on human perioral directional sensitivity.

The capacity of 8 neurologically healthy adults to distinguish direction of motion on the skin overlying the mental foramen was determined. The velocity, orientation, and the length and width of skin traversed by the moving tactile stimuli were precisely controlled. Directional sensitivity, d', was found to depend on both stimulus velocity and the length of skin traversed. Since the relationship between d' and velocity at each traverse length was well described by a generalized gamma function, it was possible to quantitatively characterize the effects of changes in traverse length on the relationship between d' and velocity. Specifically, peak (i.e., maximal) directional sensitivity increased as the length of skin traversed was increased, yet the velocity which resulted in peak directional sensitivity (i.e., the optimal or model velocity) remained invariant over the range of traverse lengths investigated (0.35-1.0 cm). The effect of stimulus velocity on directional sensitivity was least at the longest traverse lengths used. The generalized gamma function model fit the relationship between directional sensitivity and velocity equally well at all traverse lengths studied. The results lead us to anticipate that stimuli of the type used in this study should prove valuable for the detection and quantification of disturbances in orofacial tactile spatiotemporal integration in patients with peripheral nerve injury.

Adolescent↗
PubMed1989

Determinants of patchy metabolic labeling in the somatosensory cortex of cats: a possible role for intrinsic inhibitory circuitry.

Despite repeated experimental demonstration that somatic stimulation leads to an intermittent, "column-like" pattern of 2-deoxyglucose (2DG) label in the somatosensory cortex, the functional significance of this pattern remains uncertain. A number of recent studies have suggested that the putative inhibitory neurotransmitter GABA may play an influential role in the cortical processing of sensory information. To test the possibility that GABA-mediated inhibitory processes might participate in the formation of the 2DG patches, the 2DG pattern obtained under "normal" experimental conditions was compared with the pattern observed when cortical inhibition was modified by topical application of the GABA antagonist, bicuculline methiodide (BIC). Under "normal" experimental conditions, we found that somatic stimulation led to an intermittent, patch like distribution of 2DG uptake in cat somatosensory cortex, which exhibited consistent features in animals studied using the same stimulus and experimental condition. Reconstructions of the stimulus-evoked activity patterns revealed that the label was confined to territories known to receive input from the stimulated body region and was organized into elongated strips. Topical application of BIC to the somatosensory cortex dramatically altered the dimension of the metabolic patches, which were often embedded in a field of elevated 2DG uptake. In BIC-treated hemispheres the average width of 2DG patches was 1266 microns, whereas the average width of patches in the opposite untreated hemisphere (elicited by identical stimuli) was 713 microns. Unfolded maps of the labeling pattern revealed that in the BIC-treated hemispheres adjacent "strips" of 2DG label tended to fuse, leading to a less intermittent distribution than that observed in the untreated hemispheres. An important role for GABA in the formation of the normal cortical response to somatic stimulation is suggested.

Animals↗
PubMed1988

The capacity of human subjects to process directional information provided at two skin sites.

The ability of human subjects to discriminate direction of tactile stimulus motion on the dorsum of the hand was determined (1) in the absence and (2) in the presence of a moving stimulus delivered to a second skin site on the ipsilateral or contralateral forelimb. When the two skin sites were simultaneously contacted by stimuli moving in the same direction, directional sensitivity was typically below that predicted for a hypothetical subject who could independently process the information provided at each of the two skin sites. Even when the stimulus delivered to a second site was deliberately ignored, it could still alter a subject's perception of stimulus direction on the dorsal hand. Moreover, its influence was greatest whenever it moved in a direction opposite to that of the attended stimulus. Whenever the two moving stimuli were delivered nonsimultaneously to two skin sites, directional sensitivity rarely matched the levels predicted for a hypothetical subject who could independently process the information provided at each site. This, in part, resulted from the subjects' utilization of "long-range" cues provided by the temporal order of stimulation. Subjects frequently failed to distinguish these cues from the sensation of stimulus direction provided at each skin site.

Afferent Pathways↗
PubMed1988

Discrimination and scaling of velocity of stimulus motion across the skin.

The capacity of human subjects to discriminate and to scale the velocity of tactile brushing stimuli was assessed. Signal detection and classical psychophysical techniques were employed to estimate the Weber fraction over a wide range of velocities (from 1.5 to 140 cm/sec). In addition, free magnitude estimates of (1) the velocity and (2) the duration of moving tactile stimuli were obtained. It was found that human capacity to discriminate stimuli delivered to a 4 to 6-cm chord of skin on the dorsal forearm and differing in velocity remains grossly constant over the range of velocities tested and is relatively poor (i.e., the Weber fraction = 0.2-0.25). A simple power function (exponent = 0.6) satisfactorily describes the psychophysical relation (1) between the perceived and actual velocity and (2) between the perceived and actual duration of these stimuli. Since a direct proportionality between the reciprocal of a subject's estimate of duration and his or her estimate of velocity was observed, it is suggested that these two sensory attributes may reflect the operation of a neural mechanism sensitive to the duration of stimulation. Moreover, the data are inconsistent with the hypothesis that the subjects computed estimates of mean velocity from the ratio of perceived distance to perceived duration.

Acceleration↗
PubMed1988

Neural mechanisms of absolute tactile localization in monkeys.

Macaca nemestrina monkeys were trained to indicate the location of suprathreshold tactile stimuli delivered to the glabrous skin of either foot. The testing paradigm involved self-initiated trials (a bar press), followed by 10-Hz stimulation at one of six locations (e.g., on the distal phalanx of the second toe on the left foot), providing the opportunity for the animal to press one of six buttons located on a facing panel. The buttons were positioned on a picture of a monkey's feet at locations corresponding to the skin loci that were stimulated on different trials. If the animal first pressed the button corresponding to the position stimulated, liquid reward was delivered; responses to any other button terminated stimulation without reward, requiring initiation of another trial for the opportunity to receive reinforcement. The localization errors for normal monkeys were reliably greater along the mediolateral dimension of the foot than they were proximodistally. For example, stimulation of the tip of toe 4 elicited responses to the button at the tip of toe 2 on 25% of the trials, as compared with only 10% errors between the tip of toe 4 and the pad at the base of toe 4. Following unilateral interruption of the dorsal spinal columns at an upper thoracic level, the capacity for absolute tactile localization was unchanged over months of testing. The greater localization accuracy along the proximodistal axis of the foot remained after dorsal column transection. In order to evaluate neural substrates of localization by monkeys, single-neuron receptive field (RF) sizes and distributions within the first somatosensory (SI) cortex were examined to determine the overlap or separation of the representations of different points on glabrous skin. The sample of neurons that provided the RF data was obtained in previous investigations of unanesthetized, neuromuscularly blocked Macaca fascicularis monkeys. Analysis of RF overlap revealed that greater than 50% of cytoarchitectural area 1 units that responded to stimulation of one digit tip also responded to another digit or to the pad at the base of a digit. These large RFs seem poorly suited to subserve a high degree of spatial localization and are compatible with the frequent localization errors by the monkeys in the behavioral experiments. However, the area 1 RF data do not explain the tendency of these animals to exhibit better localization accuracy along the proximodistal axis than along the mediolateral axis of the volar foot.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

A combined 2-deoxyglucose and neurophysiological study of primate somatosensory cortex.

The metabolic activity pattern produced in the primary somatosensory cortex (SI) of primates by repetitive delivery of a tactile stimulus is distinctly patchy. The functional significance of these patches, however, remains obscure. This investigation sought to determine the correlation between neural and metabolic activity produced by tactile stimuli and to evaluate the relationship, if any, between the neural activity and metabolic patches evoked by similar stimuli. Experiments were undertaken in which extracellular microelectrode recordings were carried out in animals that subsequently underwent a 2-deoxyglucose (2DG) study. Three types of relations were identified. First, the receptive fields (RF) and modality properties of neurons sampled in locations at which patches of metabolic label were found matched the "place" and "modal" properties of the stimulus used to produce 2DG labeling. Second, in cortical locations where the RF and modality properties of the sampled neurons differed from either the place or modal properties of the stimulus used to evoke the 2DG label, no above-background increases in metabolic labeling were found. Finally, in some cortical locations at which the receptive field and modality properties of the neurons matched those of the 2-deoxyglucose mapping stimulus, no above-background increases in metabolic labeling were found. This outcome leads us to suggest that moment-to-moment changes in neural responsivity, which might remain undetected by conventional receptive field mapping methods, contribute to the patchy pattern of metabolic activity visualized by the 2-deoxyglucose method.

Animals↗
PubMed1987

Evidence for a mosaic representation of the body surface in area 3b of the somatic cortex of cat.

A discontinuous representation of the forelimb body surface in area 3b is proposed. Two different methods were used: single-neuron receptive-field (RF) mapping in unanesthetized cats (maximal RF) and multiunit RF mapping in deeply anesthetized cats (minimal RF). Ten or more maximal RFs were sampled in each of 14 near-radial microelectrode penetrations. In 6 penetrations, the maximal RFs of all sampled neurons (despite prominent variations in RF size and shape) shared in common a small skin area--termed the "RF center." Each of the remaining penetrations had to be divided into at least two segments (6 penetrations) or three segments (2 penetrations), for all maximal RFs mapped in a segment to include a common skin site. In six penetrations, after maximal RFs were mapped, deep general anesthesia was induced and minimal RFs were mapped in the same penetration at cortical sites separated by 150 microns. Minimal RFs closely matched the RF centers defined by maximal RFs in the same penetration. In penetrations that mapped two or three RF centers, a rapid transition in minimal RF position was detected at the same cortical site where the shift in RF center was detected. Closely spaced penetrations revealed discrete cortical columns, having the size and shape of 350- to 400-microns-diameter irregular hexagons, such that the identical minimal RF was mapped at any site within a column. The forelimb body surface in cat 3b thus appears to be represented by a mosaic of discrete columns--an organization similar to the whisker representation in rodent primary somatosensory cortex.

Animals↗
PubMed1986

Dependence of subjective traverse length on velocity of moving tactile stimuli.

Two series of experiments were performed to assess the effects of stimulus velocity on human subjects' perception of the distance traversed by a moving tactile stimulus. In all experiments, constant-velocity stimuli were applied to the dorsal surface of the left forearm; velocities ranging between 1.0 and 256 cm/sec were used. In some experiments the stimuli moved from distal to proximal over the skin, and in others they moved from proximal to distal. The length of skin contacted by the moving stimulus was defined by a plate having an aperture of 4.0 X 0.5 cm. In the first series of experiments, subjects were required to compare the distance traversed by a test stimulus delivered 2 sec after a standard stimulus, and also to report the on-locus and the off-locus of the brushing stimulus. In the second series of experiments, the subjects rated the perceived distance on the skin using a free-magnitude-estimation procedure. The data from both series of experiments defined the same relationship between stimulus velocity and perceived stimulus distance. More specifically, although the length of skin contacted by the stimulus was the same at all velocities, subjects' estimates of stimulus distance decreased with increasing stimulus velocity. In addition, the function relating estimates of stimulus distance to velocity was flat for velocities between 5 and 20 cm/sec, but possessed an appreciable negative slope at lower and higher velocities. It is interesting that the plateau of the relationship between perceived stimulus distance and velocity occurred within the range of velocities that human subjects employ to scan textured surfaces; it also corresponded precisely with the range of stimulus velocities at which the directional sensitivity of somatosensory cortical neurons and human subjects is optimal.

Adult↗
PubMed1985

Sensorimotor cortical projections to the primate cuneate nucleus.

The organization of the corticocuneate pathway was investigated in monkeys by using the anterograde and retrograde axonal transport of either horseradish peroxidase (HRP) or wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Injection of either tracer into the precentral cortex (centered on area 4) results in heavy anterograde labeling in the tegmental region, which lies immediately ventrolateral to the cuneate nucleus, particularly at levels caudal to the obex. On the other hand, injections of the same tracers involving areas 3b, 1, and 2 cause anterograde labeling mainly within the core (pars rotunda of Ferraro and Barrera, '35, Arch. Neurol. Psychol. 33:262-75) of the cuneate nucleus. Anterograde labeling is also evident in the rostral parts of the cuneate nucleus, especially after injections involving areas 1 and 2. Injections restricted largely to area 3b cause anterograde labeling preferentially in the core of the cuneate nucleus. After injection of HRP or WGA-HRP into the dorsal medulla, retrogradely labeled neurons are present both in the pre- and postcentral gyrus, but their location depends upon the sites and extent of the injection site. When the tracer diffuses into the underlying tegmental area, many retrogradely labeled neurons appear in the precentral motor cortex, principally in area 4 although some of them also occur in area 6. With smaller injections, largely restricted within the cuneate nucleus, most labeled neurons are present in the postcentral gyrus, with the largest population in areas 1 and 2; a smaller number of small neurons in area 3b are best demonstrated with WGA-HRP; and area 3a contains the smallest complement of retrogradely labeled neurons. The data from these studies suggest a segregation of pre- and postcentral afferents in the ventral tegmental region and the cuneate nucleus, respectively. These findings pertaining to the corticocuneate projection in the monkey are discussed in relation to the parallelism between monkeys and cats possible physiological implications of the anatomical organization described, and conflicting evidence in the neurophysiological observations obtained, by earlier investigators, by antidromic and orthodromic activation of this pathway.

Animals↗
PubMed1985

Metabolic labeling associated with index finger stimulation in monkey SI: between animal variability.

Four monkeys (Macaca fascicularis) were stimulated with an identical intermittent vertical displacement (flutter) stimulus on the tip of the index finger and received intravenous [14C]2-deoxyglucose (2-DG). The majority of metabolic labeling was found to exist in areas 3b and 1 of the anterior parietal cortex (SI) in the form of intermittent patches, which extended vertically across the cortical laminae. When the patches were traced through adjacent sections and reconstructed to produce a 2-dimensional map, it became evident that the patches of label combined to form a complex spatial pattern consisting of strips. Although the flutter stimulus was applied to a spatially restricted peripheral field, the metabolic pattern was always complex and widely distributed within SI. Nevertheless, the 2-DG patterns produced in the different animals stimulated with the same stimulus were strikingly similar. The relationships between descriptions of the SI index finger representation based on neurophysiological mapping data and the distribution of 2-DG uptake are described. The reproducibility of the 2-DG labeling pattern and relationship to neurophysiological maps suggests that the 2-DG mapping method provides a potent and useful tool for the investigation of stimulus representation in the somatosensory cortex.

Animals↗
PubMed1985

Assessment of the capacity of human subjects and S-I neurons to distinguish opposing directions of stimulus motion across the skin.

The ability of human subjects and the capacities of single S-I neurons of macaque monkeys to distinguish opposing directions of movement over the skin were investigated by employing experimental paradigms and data analyses based on sensory decision theory (SDT). It is shown that these techniques can be utilized to provide behavioral and neurophysiological indices of directional sensitivity which have the same metric, and are amenable to statistical tests for significance. The influences of 3 different paradigms and modes of relative operating characteristic (ROC) curve construction on SDT indices of human cutaneous directional sensitivity were investigated. Response latency (RL) was used as an objective indication of certainty in all 3 paradigms; in one of the 3 paradigms the subject also rated the certainty of each report. The SDT indices of cutaneous directional sensitivity and response bias were shown to be independent of the paradigm and mode of ROC curve construction investigated, and the SDT 'Gaussian-equal variance' hypothesis was concluded to be consistent with the data provided by all 3 paradigms. A considerable amount of inter-subject as well as intra-subject variability in human cutaneous directional sensitivity is demonstrated for all subjects tested. This variability appears to be an attribute of the processes underlying the sensing of stimulus direction since it is present even when stimulus conditions are maintained constant. Experimental designs were developed which account for this variability, thus allowing detection and quantitation of the influence of variations in stimulus conditions on human directional sensitivity. It is demonstrated that for S-I neurons, an ROC curve can be generated from the responses to multiple replications of opposing directions of movement across the receptive field. The large number of stimulus presentations required to estimate directional sensitivity from ROC curves involves a prolonged period of single neuron recording that is difficult to achieve even under ideal experimental conditions. It is shown that one can obtain a reliable estimate of single neuron directional sensitivity (i.e. delta'e) using relatively few stimulus replications when mean firing rate is assumed to represent that aspect of the neural response carrying information about stimulus direction. These indices allow assessment of the selectivity of single S-I neurons for direction as stimulus parameters are varied. Examples are provided which show (utilizing delta'e) that those stimulus conditions evoking maximal firing rates from S-I neurons are often not optimal for signalling direction of movement across the skin.

Animals↗
PubMed1985

Factors influencing cutaneous directional sensitivity: a correlative psychophysical and neurophysiological investigation.

The effects of 4 parameters of moving tactile stimuli (i.e., velocity, traverse length, position and orientation) on human cutaneous directional sensitivity and on the behavior of directionally sensitive neurons in S-I of unanesthetized macaque monkeys are studied. The experimental paradigms and approaches to data analysis are based on sensory decision theory (SDT), and provide indices of single neuron and of perceptual cutaneous direction sensitivity that can be compared. Human cutaneous directional sensitivity is shown to be maximal when the stimuli move at velocities between 5 and 30 cm/s, and to fall off either at lower or higher velocities. The neurophysiological studies of the effects of velocity reveal a heterogeneity in the population of directionally sensitive S-I neurons. Some neurons are shown to exhibit maximal directional sensitivity at velocities between 5 and 30 cm/s, whereas others possess maximal directional sensitivity at lower velocities (i.e., less than 5 cm/s). Human cutaneous directional sensitivity is determined at each of 5 different forelimb regions. The data reveal that a pronounced gradient in human cutaneous directional sensitivity exists along the proximodistal axis of the forelimb, with the greatest sensitivity existing at the most distal forelimb site studied. The companion neurophysiological studies reveal that a change in the position of the moving stimulus within the receptive field of an individual directionally sensitive S-I neuron is usually accompanied by a change in the magnitude of its directional sensitivity. Two major classes of directionally sensitive S-I neurons can be distinguished on the basis of the in-field variations in directional sensitivity they exhibit. For one neuron class, preferred direction remains the same at all regions within the receptive field; these are termed 'direction invariant neurons' and they appear to be capable of signalling direction of motion unambiguously under most of the experimental conditions used in this study. For the neurons of the second class, preferred direction varies with the position of the stimulus within the receptive field; these are termed 'direction variant' neurons. Direction variant S-I neurons signal movement toward or away from a given point within the receptive field. As a consequence, a reversal in cutaneous directional sensitivity within their receptive fields can typically be demonstrated. For every direction variant neuron studied the receptive field position at which cutaneous directional sensitivity reversed was located over a joint.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1984

Light and electron microscopic evidence for a direct corticospinal projection to superficial laminae of the dorsal horn in cats and monkeys.

The anterograde transport of horseradish peroxidase (HRP) and wheat germ agglutin conjugated to horseradish peroxidase (WGA-HRP) was employed in cats and monkeys to investigate, at both the light and electron microscopical levels, the contribution of the corticospinal tract (CST) to the superficial laminae of the dorsal horn. At the light microscopic level, this approach not only confirmed the previously documented pattern of CST termination, but also revealed a sparse projection to laminae VIII and IX of the cat and a prominent projection to the most superficial parts of the brachial dorsal horn, i.e., laminae I and II. Discrete injections involving particular cytoarchitectonic areas (4, 3a, 3b, and 1-2) of monkeys showed that the superficial laminae receive their corticofugal inputs primarily from areas 3b, 1, and 2. Electron microscopic observations were made on CST fibers and boutons which were labelled, after histochemical processing, with the reaction product of anterogradely transported WGA-HRP. The labelled fibers in the superficial laminae were small (+/- 0.5 micron), and boutons established mainly axodendritic contacts, contained mostly clear, spherical, or pleomorphic vesicles, but sometimes also displayed dense core vesicles. These boutons were primarily in lamina I and outer lamina II, but not in inner lamina II. The possible role of a direct monosynaptic pathway from the cerebral cortex to the superficial laminae of the dorsal horn is discussed in relation to the previous reports that laminae I and II play a significant role in nociception.

Animals↗
PubMed1984

Neurons with unusual response and receptive-field properties in upper laminae of cat SI cortex.

High-impedance micropipettes are used to record (both extra- and intracellularly) the electrical activity of neural elements located 550 micron or less from the pial surface of cerebral cortical areas 3a, 3b, 1, and 2 in unanesthetized cats. These elements are designated as "upper-layer SI units" and most frequently are sampled within the arm and forelimb digit sectors of areas 3b and 1. Mechanical stimulation of the skin is employed to determine the receptive field (RF) and response properties of the upper-layer units sampled. Single-shock electrical stimulation of the skin is used to obtain estimates of the minimal latency for eliciting spike discharge. Intracellular iontophoretic injection of horseradish peroxidase (HRP) is used to determine the laminar locations of the somata of the neural elements from which recordings are obtained. The receptive field (RF) and response properties of most upper-layer units sampled in areas 3b and 1 differ substantially from those of units recorded at depths greater than 550 micron from the pial surface in the same cortical fields. The members of one group of upper-layer area 3b and 1 units (U units) respond best to infrequently repeated (typically less than 0.5/s), slowly moving (1-5 cm/s) tactile stimuli. For the same units, repetitive application of slow-moving tactile stimuli to the RF typically leads to an enhancement of responsiveness accompanied by an elevation of spontaneous activity. In contrast, repetitive stimuli delivered at high velocity and at short interstimulus intervals lead to a decrease in unit responsiveness and to an absence of spontaneous activity. The members of a second group of upper-layer units (R units) respond best to moving stimuli delivered at higher velocities (5-20 cm/s), respond reliably at stimulus repetition rates well in excess of 0.5/s, and do not exhibit pronounced changes in responsiveness to repeated stimulation. The RFs of most upper-layer units (both R and U units) involve restricted regions on the contralateral upper limb, but the RFs of U units have poorly defined borders. In addition, the distribution of sensitivity within the RF of at least some U units is nonuniform and, frequently, discontinuous. Contralateral as well as ipsilateral body regions are included within the RFs for 12% of the upper-layer neurons sampled; the remainder (8%) have RFs restricted to the contralateral body.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Patterns of metabolic activity in cytoarchitectural area SII and surrounding cortical fields of the monkey.

The pattern of [14C]2-deoxyglucose (2-DG) labeling evoked by tactile stimuli was determined in cerebral cortical cytoarchitectural area SII and the fields that surround it (including area 7b, the retroinsular field (Ri), and the granular insular region (Ig) for a series of nine monkeys (macaca fascicularis). In all animals and for all tactile stimuli, the cortical labeling most frequently occurred in the form of patchlike aggregates of metabolically active neurons. Individual patches typically included laminae II-V, were most densely labeled in the central layers, and possessed limited tangential width. Analysis of the relations between patches of label in adjacent sections revealed that the metabolically active neurons form three-dimensional aggregates (termed modules or strips), which can extend for several millimeters. It is hypothesized that these metabolic modules may correspond to information-processing units within the cerebral cortex. Two-dimensional reconstructions of the 2-DG label in the hemispheres ipsilateral and contralateral to the somatic stimuli reveal that the strips of high metabolic activity are interspersed with regions of substantially less activity. In all cortical regions examined in this study, the strips were oriented roughly from anterior to posterior. Systematic changes in the place of the somatic stimulus led to systematic changes in the cortical location of the strips of metabolic label. Conversely, animals subjected to nearly identical tactile stimuli produced very similar patterns of metabolic activity. Comparison of the distribution of metabolic activity in area SII of the hemispheres ipsilateral and contralateral to the stimulus demonstrated that although the amount of labeling in SII ipsilateral to the stimulus was typically less than that present in SII of the contralateral hemisphere, it was both substantial and topographically highly organized. The labeling in the cytoarchitectural zones surrounding SII (i.e., 7b, Ri, and Ig), although clearly stimulus related, occupied extensively overlapping regions in all experiments even though the body regions stimulated were in widely different locations. As a result, a relative lack of topographical organization within these cortical fields is indicated.

Animals↗
PubMed1983

The corticocuneate pathway in the cat: relations among terminal distribution patterns, cytoarchitecture, and single neuron functional properties.

A combined anatomical and physiological strategy was used to investigate the organization of the corticocuneate pathway in the cat. The distribution of the corticocuneate projection was mapped by means of the anterograde horseradish peroxidase (HRP) labeling technique and correlated with the nuclear cytoarchitecture in Nissl and Golgi material, the distribution of retrogradely labeled relay cells after HRP injections in the ventrobasal complex of the thalamus, and the topographic organization derived from single- and multiunit recordings in the decerebrate, unanesthetized cat. This approach provided details about the arrangement of the corticocuneate pathway that were not available from previous studies with anterograde degeneration methods. On the basis of cytoarchitectonic and connectional features, a number of subdivisions are identified in the cuneate nucleus, each of which is associated with characteristic functional properties. In agreement with previous studies, it is found that a large portion of the cuneate nucleus, the middle dorsal part (MCd), is exclusively devoted to the representation of cutaneous receptive fields on the digits. This "core" region contains more thalamic projecting neurons than any other subdivision of the cuneate nucleus. A topographic arrangement also exists in the subdivisions of the rostral cuneate and of the nuclear region ventral to MCd, although in these, receptive fields are larger and predominantly, but not exclusively, related to deep receptors and involve the arm, shoulder, and trunk. Observations on corticocuneate projections were based on injections, mainly focused on functional subdivisions of the primary somatosensory cortex (SI) as described by McKenna et al. (1981). Although cortical projections are mainly to cuneate regions other than its core, a significant proportion of fibers from the region of SI where the digits are represented (particularly area 3b) do project to the MCd region of the cuneate nucleus. Similarly, nuclear areas associated with receptive fields on the arm and trunk are labeled after injection in SI arm and trunk regions, respectively. Thus, a close topographic relationship appears to exist between the somatosensory cortex and cuneate regions related to the same body representation, although nuclear regions in which receptive fields on the neck area are represented receive very sparse or no detectable cortical projections even when the injection of the tracer involves the entire sensorimotor cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗