Cortical Area 3b

More than 350 neurons with fingerpad receptive fields (RFs) were studied in cortical area 3b of three alert monkeys.  

Cortical reorganization of the subtly differentiated hand map after peripheral nerve injury might be better understood if there was a topographic conception of the homuncular representation of the dorsal finger surfaces in humans, in addition to the well-established sequential rostrocaudal array of the ventral finger aspects in cortical area 3b.  

The most substantial effect of the sensory environment was on receptive field sizes in cortical area 3b.  

We determined the somatotopy of the face and the oral cavity representation in cortical area 3b of New World owl monkeys and squirrel monkeys.  

This same overall pattern of reorganization was present in the deprived hand representation of cortical area 3b.  

We used the P20-N20 dipole evoked by electrical stimulation of the median nerve at the wrist, corresponding to synaptic activity within cortical area 3b, as a local spatial reference to examine the contributions of the pre- and postcentral cortex.  

This is the third in a series of studies of the neural representation of tactile spatial form in somatosensory cortical area 3b of the alert monkey.  

These data were then compared with analogous data from our earlier cortical area 3b studies, which used the same approaches and acute injury, to assess relationships of cuneate and cortical changes.  

In cortical area 3b, the magnification of representation of these differentially engaged glabrous fingertip surfaces was nearly 2x larger than for the corresponding surfaces of other hand digits, or for the contralateral cortical representations of the same digit surfaces on the opposite hand. Thus, with very limited manual exercise over a total period of a few hours of practice at a skill played out in brief daily sessions over a several week long training period, the representations of skin surfaces providing information crucial for successfully performing a small-object retrieval behavior appeared to be substantially remodeled in the most 'primary' of the SI somatosensory cortical fields, cortical area 3b.  

This is the second in a series of studies of the neural representation of tactile spatial form in cortical area 3b of the alert monkey.  

Behavioral observations along with positive changes in the cortical area 3b representations of specific skin surfaces implicated specific glabrous finger inputs as important contributors to skill acquisition.  

We examined sensory afferent terminations in the spinal cord and brainstem, and determined the somatotopic organization of cortical area 3b in three adult monkeys with previous hand or forearm amputation, as veterinary treatment of forelimb injuries.  

Isolated receptive fields across the mediolateral extent of cortical area 3b were highly unusual with respect to normal topography, but they were completely consistent with the hypothesis that the correlated activation of peripheral afferents acts to shape expressed cortical receptive fields..  

These territories were then related to cutaneous receptive fields of cortical area 3b neurons to determine how low-threshold inputs from each hand nerve map onto the primary somatosensory cortex.  

The rostrocaudal extent of the thalamic territory defining the soma distribution of neurons projecting to small zones of cortical area 3b was similar, but typically extended into the ventral part of VPLc, filling out a medially concavo-convex laminar space.  

Features of organization in the cortical area 3b hand map were then assessed with neurophysiological mapping procedures, and compared to features in monkeys that had undergone either a normal postnatal development with three intact hand nerves, or an abnormal development with two intact nerves due to postnatal injury of the median nerve.  

Following periods of 0.4-1.5 years, features of organization in the cortical area 3b hand map were assessed neurophysiologically, and compared to features in normally reared monkeys.  

The sharpening of the response of cortical area 3b neurons relative to the period of the stimulus could be accounted for by a large subpopulation of neurons that had highly coherent responses.  

The distributed responses of cortical neurons ("maps") of the hand surfaces were defined in detail in somatosensory cortical area 3b.  

In cortical area 3b of monkeys, responses of 71 single neurons to controlled indentations of glabrous skin were recorded before and during iontophoretic application of GABA and bicuculline methiodide (BMI), a GABA receptor antagonist.  

Multiple microelectrode maps of the hand representation within and across the borders of cortical area 3b were obtained before, immediately after, or several weeks after a period of behaviorally controlled hand use.  

These examples include representation remodeling in cortical area 3b following digit amputation, digit fusion, local intracortical microstimulation, restricted cortical lesions, or as a consequence of behaviorally controlled stimulation of restricted hand surfaces.  

In cortical area 3b of cats, responses of 76 single neurons to punctate indentations were recorded before and during iontophoretic administration of bicuculline methiodide (BMI), a GABAergic antagonist, at levels that did not affect spontaneous activity.  

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.  

Anatomical tracers were injected into electrophysiologically defined sites in somatosensory cortical area 3b (SI proper) and Area I (posterior cutaneous field) of owl monkeys after these cortical subdivisions had been extensively explored in microelectrode mapping experiments.  

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