We recorded the activity of parietal area 7a neurons in monkeys performing an object construction task. In each trial, a model object consisting of a variable arrangement of squares was presented, followed after a delay by a copy of the model object that was missing a single square. Monkeys replaced the missing square to reconstruct the model configuration. Activity of many 7a neurons varied systematically with the position of the missing square and predicted where monkeys were going to add parts to the object they were building. The location of the missing square was a computed spatial datum important to object construction which did not correlate with the retinal location of a visual stimulus or the direction of the required motor response. The population of cells coding this coordinate was generally inactive when the same spatial locations were made relevant by visual targets to which monkeys either planned saccades or directed attention in other behavioral contexts. The data suggest that some parietal neurons participate in neural representations of space that reflect spatial cognitive as opposed to sensorimotor processing, coding the results of spatial computations performed on visual stimuli to meet cognitive objectives.
Bibliographical noteFunding Information:
In the present experiment, we investigated neural activity in parietal cortex during object construction. Our choice of this behavior for study was motivated by evidence that parietal damage can interfere with a person’s ability to assemble or construct objects, while sparing basic motor function. This defect in the spatial organization of movement is known as constructional apraxia (Kleist, 1934), and follows damage to various cortical areas (Benson and Barton, 1970; Arena and Gainotti, 1978; Carlesimo et al., 1993), but is most common and severe following lesions of the right posterior parietal cortex (Black and Strub, 1976; Villa et al., 1986; Ruessmann et al., 1988). Consequently object construction is likely to depend at least in part on spatial processing normally supported by the intact posterior parietal cortex.
- Area 7a
- Constructional apraxia
- Spatial attention
- Spatial cognition