Effects of spinal tractotomy on spatial sequence recognition in macaques

Abstract

Five Macaca speciosa monkeys were trained to discriminate between the order of two tactile stimulus presentations (proximal-distal vs. distal-proximal) to the lateral calf. Psychophysical thresholds for tactile sequence recognition were obtained by varying the distance between the spots stimulated. Stabilized preoperative thresholds for stimulation on the lateral calf averaged 10.4 mm, which is comparable to point localization thresholds for sequential contact of the proximal limbs of humans. Complete interruption of the ipsilateral fasciculus gracilis produced elevations of thresholds within the first 3 postoperative weeks to an average of 3.6 times the control values. With training over 6 postoperative months, normal discrimination recovered. In contrast to the effects of dorsal column (DC) lesions, interruption of the lateral and ventral columns ipsilaterally or contralaterally produced no deficit or a mild and transient deficit. Monkeys with isolation of either the ipsilateral dorsolateral column (ILC) or the contralateral ventral quadrant (CVQ) exhibited substantial and enduring deficits. Thresholds were elevated an average of 5 times the control values, and recovery was not observed or was incomplete after months of training. In contrast, isolation of the ipsilateral dorsal column produced little or no threshold elevation. The results of isolating lesions complement the series of primary lesions to each cord sector, showing that spatiotactile sequence recognition for the hindlimb is served more critically by the dorsal columns than by the lateral columns.

Impaired detection of repetitive stimulation following interruption of the dorsal spinal column in primates

“…Most investigations that have employed suprathreshold levels of cutaneous stimulation have not observed enduring de® cits as a result of selective interruption of the DC pathway on behavioral tests of tactile capacities (Cook and Browder, 1965;Schwartz et al, 1972;Vierck, 1973Vierck, , 1977Azulay and Schwartz, 1975;Vierck et al, 1983Vierck et al, , 1988Vierck and Cooper, 1990). However, several investigators have noted that DC-lesioned animals fail to respond on some trials or in certain situations (Schwartzman and Bogdonoff, 1969;W all, 1970), FIGURE 1.…”

“…Similarly, spatiotactile tests with a higher degree of resolution (lower thresholds) have revealed only temporary impairments. De® cits have been observed for tactile size discrimination and point localization (Vierck, 1973;Vierck et al, 1983), but recovery to normal performance was observed with extended postoperative training. It is clear from the lack of permanent de® cits on these tasks that somatotopically precise input is provided to supraspinal targets by spinal pathways in the ipsilateral and contralateral lateral columns (Andersson, 1962;Eidelberg and W oodbury, 1972;Dreyer et al, 1974).…”

Role of primary somatosensory cortex in the coding of pain

“…In contrast, spatiotactile localization and discrimination remain normal [122;124]. This sparing of spatial discrimination, coupled with the loss of cortically derived functions dependent upon stimulus movement, repetition or duration is compatible with high resolution 2-deoxyglucose metabolic maps of SI responses to tactile stimulation [113].…”

Significance of adequate postural control in the appearance of habitual upright bipedal locomotion

“…Another cutaneous mechanoreceptor, Mercel complex, is frequently absent in human skin of digits, and in one case its density was 3.9-4.1/mm 2 [42], which corresponds to its density in M. fascicularis [43]. Discrimination of spatial sequence on the hairy skin of macaque hind limbs is comparable to human thresholds for point localization [44]. Ability of SI cortical neurons of the rhesus monkey to discriminate velocity of brush movement across the glabrous skin of the hand may be the same as in humans [45].…”