John T. Wall

Consistent features of the representation of the hand in area 3b of macaque monkeys.

Multiunit microelectrode recordings were used to explore the responsiveness and somatotopic organization of the representation of the hand in area 3b of anesthetized macaque monkeys. Major findings were as follows: Recording sites throughout the hand representation were activated by low-threshold cutaneous stimulation. Simple, punctate mechanical stimuli were highly effective in activating neurons. Neurons had small, restricted receptive fields. Representations of nearly all skin surfaces of the hand were demonstrated in individual monkeys. The basic topographic pattern found in all monkeys included the following: a large sequential representation of the glabrous digits from thumb to little finger from lateral to medial in cortex, and from proximal to distal hand parts in cortex extending down the caudal bank of the central sulcus; moderately large representations of radial and ulnar pads of the palm in respective lateral and medial cortical locations in the hand representation; and a relatively small, fragmented representation of the dorsal hand and dorsal digits, with the fragments interspersed within the representation of the glabrous hand. The proportions of the proximal, middle, and distal glabrous digits varied, so that the representation of the distal phalanx sometimes approached the dorsal border of area 3b with area 1. A comparison of the present findings with previous results from macaque monkeys indicates that the above-described features have been revealed under a variety of recording and anesthetic conditions. Consistencies in previous and present results strongly support the conclusions that the hand representation in area 3b of macaque monkeys is activated by cutaneous receptors throughout; is composed of neurons with relatively simple, small, cutaneous receptive fields; includes all skin surfaces of the hand; and is somatotopic for the glabrous skin with small, discontinuous, intercalated representations of fragments of the dorsal skin.

The somatotopic pattern of afferent projections from the digits to the spinal cord and cuneate nucleus in macaque monkeys

The somatotopic patterns of terminations in the spinal cord and cuneate nucleus of afferents from the digits of macaque monkeys were determined by the transganglionic transport of a mixture of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) and free horseradish peroxidase (HRP). Injections placed in either a single digit or in various combinations of digits indicate that terminations from the digits are located medially in the superficial laminae of cervical segments 5-7 in the dorsal horn. Each digit has a distinct zone of terminations, and inputs from D1-D5 terminate in order in a rostrocaudal sequence. In the cuneate nucleus, afferents from single digits are ventrally situated and organized into rostrocaudally elongated columns of label. In the pars rotunda of the cuneate nucleus, the representations of the digits appear to be offset from one another with D1 represented most laterally, and the other digits represented in order progressively more medially. In portions of the cuneate nucleus rostral and caudal to the pars rotunda, the projections from the digits are more diffuse and overlap one another.

Representations of the face, teeth and oral cavity in areas 3b and 1 of somatosensory cortex in squirrel monkeys.

The somatotopic organization of low threshold inputs from the face and head was determined in the lateral portion of areas 3b and 1 in squirrel monkeys. A complete, topographically organized representation was found in area 3b, and a separate, roughly parallel representation was found in adjacent area 1. In addition, there was evidence for remarkable individual variability in the representation of the lips in area 3b.

Long-term cortical consequences of reinnervation errors after nerve regeneration in monkeys

Sensory innervation patterns are commonly altered after nerve regeneration, but the long-term consequences of these peripheral changes on the central nervous system are not understood. We report here that when innervation patterns to the hands of two adult monkeys were changed by cross-repair of nerves, topographical features that were clearly related to the new innervation pattern remained apparent in primary somatosensory cortical area 3b as long as 2.9 years after repair. These findings indicate that peripheral innervation changes are not easily corrected by central circuits leading to primary cortex.

Development and Maintenance of Somatotopic Maps of the Skin: A Mosaic Hypothesis Based on Peripheral and Central Contiguities (Part 1 of 2)

The somatotopic mapping of tactile information from the skin onto structures in the brain is ubiquitous in the somatosensory system of mammals. This paper reviews evidence which suggests that the somatotopic map in the S-I cortex of the rat is not a single topographic entity but, instead, is a mosaic. This mosaic is comprised of subunits that process information from inputs which, by nature of their peripheral grouping and associated distribution to unified receptor surfaces, provide spatially and temporally contiguous signals. These subunits are developed and subsequently maintained in a piecemeal fashion within the integrated somatotopic map of the body. The relative size of the subunits is alterable by different mechanisms in newborn and adult animals.

Cortical projections of the medial visual area in the owl monkey, Aotus trivirgatus

The cortical projections of the Medial Area (M) of the owl monkey were studied using the autoradiographic method. Area M projects to several extrastriate areas, including Area 18, in a pattern of terminations unlike that which would be expected if M was part of a larger Area 19 or V III band. The pattern of terminal lamination was found to be somewhat unusual in that projections were to layers VI, I and the deep portion of layer V in the major target areas.