Sensory stimuli to the body are conveyed by the spinal cord to the primary somatosensory cortex. It has long been thought that dorsal column afferents of the spinal cord represent the main pathway for these signals, but the physiological and behavioural consequences of cutting the dorsal column have been reported to range from mild and transitory to marked. We have re-examined this issue by sectioning the dorsal columns in the cervical region and recording the responses to hand stimulation in the contralateral primary somatosensory cortex (area 3b). Following a complete section of the dorsal columns, neurons in area 3b become immediately and perhaps permanently unresponsive to hand stimulation. Following a partial section, the remaining dorsal column afferents continue to activate neurons within their normal cortical target territories, but after five or more weeks the area of activation is greatly expanded. After prolonged recovery periods of six months or more, the deprived hand territory becomes responsive to inputs from the face (which are unaffected by spinal cord section). Thus, area 3b of somatosensory cortex is highly dependent on dorsal spinal column inputs, and other spinal pathways do not substitute for the dorsal columns even after injury.

Adult brains undergo large-scale plastic changes after peripheral and central injuries. Although it has been shown that both the cortical and thalamic representations can reorganize, uncertainties exist regarding the extent, nature, and time course of changes at each level. We have determined how cortical representations in the somatosensory area 3b and the ventroposterior (VP) nucleus of thalamus are affected by long standing unilateral dorsal column lesions at cervical levels in macaque monkeys. In monkeys with recovery periods of 22-23 months, the intact face inputs expanded into the deafferented hand region of area 3b after complete or partial lesions of the dorsal columns. The expansion of the face region could extend all the way medially into the leg and foot representations. In the same monkeys, similar expansions of the face representation take place in the VP nucleus of the thalamus, indicating that both these processing levels undergo similar reorganizations. The receptive fields of the expanded representations were similar in somatosensory cortex and thalamus. In two monkeys, we determined the extent of the brain reorganization immediately after dorsal column lesions. In these monkeys, the deafferented regions of area 3b and the VP nucleus became unresponsive to the peripheral touch immediately after the lesion. No reorganization was seen in the cortex or the VP nucleus. A comparison of the extents of deafferentation across the monkeys shows that even if the dorsal column lesion is partial, preserving most of the hand representation, it is sufficient to induce an expansion of the face representation.

Somatotopic maps in the cortex and the thalamus of adult monkeys and humans reorganize in response to altered inputs. After loss of the sensory afferents from the forelimb in monkeys because of transection of the dorsal columns of the spinal cord, therapeutic amputation of an arm or transection of the dorsal roots of the peripheral nerves, the deprived portions of the hand and arm representations in primary somatosensory cortex (area 3b), become responsive to inputs from the face and any remaining afferents from the arm. Cortical and subcortical mechanisms that underlie this reorganization are uncertain and appear to be manifold. Here we show that the face afferents from the trigeminal nucleus of the brainstem sprout and grow into the cuneate nucleus in adult monkeys after lesions of the dorsal columns of the spinal cord or therapeutic amputation of an arm. This growth may underlie the large-scale expansion of the face representation into the hand region of somatosensory cortex that follows such deafferentations.primate ͉ somatosensory ͉ sprouting ͉ plasticity ͉ dorsal columns I n adult monkeys and other mammals, a loss of afferents from the skin is followed by reorganization of the somatosensory cortex so that lost inputs are replaced by intact inputs in the representation (1, 2). Massive losses of inputs lead to large-scale reorganizations such that the somatotopic boundaries in the cortex may shift by more than 10 mm (3, 4). Such reorganizations in sensory representations probably depend on multiple mechanisms, including the potentiation of remaining synapses, the unmasking of latent connections by disinhibition, and possibly the growth of axon arbors and dendrites (5-10). However, there is little direct evidence for the mechanisms that mediate largescale reorganizations. We presumed that neuronal growth may play an important role in reorganizations where response to the face inputs expands into the hand region of area 3b because the expansion of the receptive fields is beyond any known limits of normal spread of thalamocortical or corticocortical arbors (11)(12)(13)(14)(15). Moreover, our experiments showed that the emergence of responses to the stimulation of the chin in the deprived hand cortex takes 6-8 mo (3), a time compatible with the growth of new connections. Finally, at the lower brainstem levels, the chin representation in the trigeminal nucleus lies adjacent to the hand representation in the cuneate nucleus. A limited growth of horizontal connections is known to occur within deprived visual cortex of adult cats (10) and deprived somatosensory cortex of monkeys (9). In addition, in monkeys with arm amputations, there is evidence that afferents from the stump of the arm can grow a short distance from their normal terminations in the dorsal part of the cuneate nucleus of the brainstem to the nearby ventral part, where digit inputs normally terminate (16). The question that we address here is whether the growth of new connections in the brain is a critical component of the massive cortical reorganizat...

Aims-To evaluate the usefulness of the devR based polymerase chain reaction (PCR) in the detection of Mycobacterium tuberculosis in lymph node aspirates and tissues of lymphadenitis and to compare PCR with conventional diagnostic techniques. Subjects and methods-Coded specimens of fine needle aspirates and biopsies from 22 patients with tuberculous lymphadenitis, 14 patients with non-tubercular lymphadenitis, and nine patients with granulomatous lymphadenitis were processed and subjected to analysis by PCR, smear microscopy, M tuberculosis culture, histology, and cytology. Results-Tuberculous lymphadenitis was correctly diagnosed by PCR in 18 patients, by culture in five patients, by histology in 13 patients, and by cytology in seven patients. PCR gave two false positive results in 14 patients with non-tubercular lymphadenitis. The sensitivity of the conventional techniques was significantly higher with biopsies (17 of 22 specimens; 77%) than with fine needle aspirates (nine of 22 specimens; 41%). However, the sensitivity of PCR was not significantly higher with biopsies (68%) in comparison with fine needle aspirates (55%). The sensitivity of either biopsy PCR or fine needle aspirate PCR was not significantly diVerent from that of either histology combined with culture or cytology combined with culture. The overall combined specificity of PCR was 86%. Mycobacterium tuberculosis DNA was detected in six of nine patients with granulomatous lymphadenitis. Conclusion-PCR is the most sensitive single technique available to date for the demonstration of M tuberculosis in specimens derived from patients with a clinical suspicion of tuberculous lymphadenitis. The value of PCR lies in its use as an adjunct test in the diagnosis of tuberculous lymphadenitis, particularly in those patients where conventional methods fail. Because fine needle aspiration is not an invasive procedure, it is the procedure of choice, and PCR should be performed initially on these samples. Excisional biopsy histology and PCR should be recommended only for patients in whom fine needle aspirate PCR is negative or when there is discrepancy with the clinical impression. (J Clin Pathol 2000;53:355-361)

An isomorph of the glabrous hand is visible in primary somato-sensory cortex (area 3b) of owl monkeys in brain sections cut parallel to the surface and stained for myelin. A mediolateral row of five ovals, separated by myelin-light septa, represents digits and corresponds precisely with cortical sites activated by light touch on individual digits in microelectrode recordings. A number of caudal ovals relate to pads of the palm. A more distinct septum separates the hand from the more lateral face representation. Within the face representation, two large myelin-dense ovals can be identified that are activated by the upper or lower face in a caudo-rostral sequence. Accidental finger loss or dorsal column section, deafferentations that result in reorganization of the physiological map in area 3b, do not alter the morphological map. The proportions for each digit and palm in the morphological map do not vary across normal and deafferented animals. Similar isomorphs were also seen in area 3b of squirrel and macaque monkeys. We conclude that the anatomical isomorph for the body surface representation in area 3b is a reliable reflection of normal cortical organization and may be a common feature of the primate area 3b. The isomorph can provide a reference in studies of somatotopic reorganization.

The primary motor cortex of mammals has an orderly representation of different body parts. Within the representation of each body part the organization is more complex, with groups of neurons representing movements of a muscle or a group of muscles. In rats, uncertainties continue to exist regarding organization of the primary motor cortex in the whisker and the neck region. Using intracortical microstimulation (ICMS) we show that movements evoked in the whisker and the neck region of the rat motor cortex are highly sensitive to the depth of anaesthesia. At light anaesthetic depth, whisker movements are readily evoked from a large medial region of the motor cortex. Lateral to this is a small region where movements of the neck are evoked. However, in animals under deep anaesthesia whisker movements cannot be evoked. Instead, neck movements are evoked from this region. The neck movement region thus becomes greatly expanded. An analysis of the threshold currents required to evoke movements at different anaesthetic depths reveals that the caudal portion of the whisker region has dual representation, of both the whisker and the neck movements. The results also underline the importance of carefully controlling the depth of anaesthesia during ICMS experiments.

Adult mammalian brains undergo reorganization following deafferentations due to peripheral nerve, cortical or spinal cord injuries. The largest extent of cortical reorganization is seen in area 3b of the somatosensory cortex of monkeys with chronic transection of the dorsal roots or dorsal columns of the spinal cord. These injuries cause expansion of intact face inputs into the deafferented hand cortex, resulting in a change of representational boundaries by more than 7 mm. Here we show that large-scale reorganization in area 3b following spinal cord injuries is due to changes at the level of the brainstem nuclei and not due to cortical mechanisms. Selective inactivation of the reorganized cuneate nucleus of the brainstem eliminates observed face expansion in area 3b. Thus, the substrate for the observed expanded face representation in area 3b lies in the cuneate nucleus.

We determined the somatotopy of the face and the oral cavity representation in cortical area 3b of New World owl monkeys and squirrel monkeys. Area 3b is apparent as a densely myelinated strip in brain sections cut parallel to the surface of flattened cortex. A narrow myelin-light septum that we have termed the "hand-face septum" separates the hand representation from the more lateral face and mouth representation. The face and oral cavity representation is further divided into a series of myelin-dense ovals. We show that three ovals adjacent to the hand representation correspond to the upper face, upper lip, and chin plus lower lip, whereas three or four more rostral ovals successively represent the contralateral teeth, tongue, and the ipsilateral teeth and tongue. Strips of cortex lateral and medial to the area 3b ovals, possibly corresponding to area 1 and area 3a, respectively, have similar somatotopic sequences. Although previous results suggest the existence of great variability within and across primate species, we conclude that the representations of the face and mouth are highly similar across individuals of the same species, and there are extensive overall similarities across these two species of New World monkeys.