Spatial working memory capacity in unilateral neglect

Abstract

It has been proposed recently that a deficit in keeping track of spatial locations may contribute to the severity of unilateral neglect in some right hemisphere stroke patients. However, performance on traditional spatial working memory (SWM) tasks (e.g. Corsi blocks) might be confounded by failure to encode leftward locations, rather than a true deficit of maintaining locations in SWM. Here we introduced new procedures for circumventing this to measure SWM capacity in neglect. In a first experiment, 20 right hemisphere stroke patients (10 with and 10 without neglect) were tested on a computerized vertical variant of the Corsi task. Sequences of spatial locations in a vertical column were displayed and participants had to tap out the remembered sequence on a touchscreen. Patients with left neglect were impaired on this vertical SWM task compared with all control groups. However, poor performance on this task (as for Corsi blocks) might involve impaired memory for stimulus sequence, or poor visuomotor control of manual responding, rather than reduced SWM capacity per se. A second experiment therefore employed a purer measure of vertical SWM. After the displayed sequence, a single location was now probed visually, with observers judging verbally (yes/no) if it had been in the preceding sequence. Hence order no longer mattered, and no spatial motor response was required. Again, the neglect group was impaired relative to all others, now with very little overlap between the performances of individual neglect patients versus individuals in control groups. Poor performance on the second task, which provides a purer measure of SWM capacity, correlated with severity of left neglect on cancellation tasks (but not on line bisection), consistent with recent proposals that SWM deficits can exacerbate left neglect on visual search tasks when present conjointly. Lesion anatomy indicated that neglect patients with a SWM deficit were most likely to have damage to parietal white matter, plus, in the second experiment, to the insula also. These findings demonstrate that an impairment in SWM capacity can contribute to the neglect syndrome in patients with stroke involving regions within the right parietal lobe and insula.