Each maze contained a central start box, from which a single path (referred to as the main path) extended through the maze. On one-half of trials, the selleck inhibitor main path reached an exit in the maze perimeter (Fig. 8A; ‘Exit’). On the remaining half of trials, the main path reached a blind ending (Fig. 8A; ‘No exit’). The monkey was
required to determine whether the main path reached an exit or blind ending, and press one of two response keys to indicate their judgment. The task was intended to recruit a covert analysis of the spatial structure of the maze, specifically of the main path. The radial direction of the main path varied randomly over trials, and was either straight (Fig. 8A; ‘Straight main path’), or contained a single 90° turn (Fig. 8; ‘One-turn main path’). During the performance of this task, many parietal neurons were robustly activated at the onset of the maze as a function of the direction of the main path that was mentally tracked (Fig. 8B; Crowe et al., 2004). As in the construction task, neurons active in the maze task generally carried spatial information only during maze solution, and were not active during simpler sensorimotor tasks in which monkeys planned eye movements in directions that corresponded selleck chemicals llc to the path directions during maze solution (Crowe et al., 2004). When monkeys mentally tracked
a path that turned, the neuronal population vector constructed from spatially tuned neurons in area 7a rotated in the direction of the turn as the mental analysis of the maze progressed (Fig. 8C; Crowe et al., 2005), when no movements were made and
no changes in the visual input occurred. Neural data from the construction and maze tasks provide convergent evidence that spatial information processing in parietal cortex can be decoupled from the spatial attributes of stimuli and movements in order to Urocanase support a cognitive process, as distinguished from a sensorimotor one. Both experiments demonstrate that parietal neurons contribute to a covert analysis of the visual input that extracts the embedded spatial information specifically needed to achieve a behavioural goal. In addition to the impairments in visuomotor control and spatial cognition reviewed above, damage particularly to right parietal cortex disrupts the conscious awareness of visual space, producing a syndrome referred to as hemispatial neglect (Gainotti et al., 1972; Colombo et al., 1976; Bisiach et al., 1979; Adair & Driver & Halligan, 1991; Driver et al., 1992). Neglect is not a symptom that is limited to damage of parietal cortex, however, and the locus of the lesion producing the strongest neglect is controversial, with some studies placing this locus in the temporal cortex (Karnath et al., 2001). Patients with this disorder fail to consciously perceive stimuli or events that occur in the side of space opposite their damaged cerebral hemisphere.