Perceptual, premotor and motor factors in the performance of a delayed-reaching task by subjects with unilateral spatial neglect.

We used a computerized delayed-reaching task with a simple reaction time (RT) to investigate the visuo-motor and spatio-temporal performance of right brain-damaged (RBD) patients with unilateral spatial neglect (USN). Fifty-three RBD patients (22 with and 31 without USN) and 25 controls performed the tasks. We recorded the following data: the first RT (RT-1), which is thought to reflect the detection of the target position (the perceptual factor); the second RT (RT-2), which represents the initiation of reaching (the motor initiation aspect of premotor factors); the movement time (MT), which is hypothesized to reflect the "pure" motor component of the task. RBD patients with both USN and hemianopia demonstrated significantly longer RTs towards the left than towards the right for both the RT-1 and the RT-2. Among the RBD patients without hemianopia, the laterality index (left side/right side) of the RT-1 in those with USN was significantly greater than in those without USN or the controls. Among the three groups, there were no significant differences between the laterality indices of either the RT-2s or the MTs. These results suggest that the impairment of leftward movement in RBD patients with USN might be caused primarily by a perceptual impairment rather than an impairment in motor initiation, and is certainly not a "pure" motor impairment.

Visual receptive fields and movement fields of visuomovement neurons in the monkey premotor cortex obtained during a visually guided reaching task.

Single-neuron activity in the premotor cortex of monkeys was examined while they performed a visually guided reaching task with their eyes fixated. We recorded a total of 177 visually responsive neurons that showed significantly enhanced activity after a presentation of visuospatial cue ('visual response'). Of these neurons, 57% (n = 101) also showed significantly enhanced activity after an onset of the go-signal and before movement ('movement-associated response'). These were designated as 'visuomovement neurons'. The visual response latencies of 81% of the visuomovement neurons were between 60 and 160 ms (median = 100 ms) and the response durations were less than 240 ms in 80% of the neurons. The preferred direction of the visual response (PDV) was toward the contralateral side in 57% and the ipsilateral side in 20% of the neurons. The preferred direction of the movement-associated response (PDM) was toward the contralateral side in 50% of the neurons. In most of the neurons (74/101, 73%), the PDV and the PDM corresponded to approximately the same direction. These results suggest that premotor visuomovement neurons play a role in receiving visuospatial information for visually guided reaching, and commanding reaching movements.

Functioning heterotopic grey matter? Increased blood flow with voluntary movement and sensory stimulation.

A 66-year-old woman with a right hemiplegia due to cerebral haemorrhage was found to have heterotopic grey matter in the left frontal and right frontal and parietal lobes. She had no neurological disturbance prior to the haemorrhage. Regional cerebral blood flow (rCBF) was measured by xenon-CT (Xe-CT) in the zones of heterotopic grey matter during voluntary movement and sensory stimulation of her left limbs. During voluntary movement, rCBF increased markedly in the heterotopic grey matter of the frontal lobes and the overlying cortex. During sensory stimulation, rCBF increased in the right parietal heterotopic grey matter and the overlying cortex. This strongly suggests that the heterotopic grey matter is functional.