Inactivation of Dorsolateral Prefrontal Cortex During Auditory Working Memory.

backgroundThe dorsolateral prefrontal cortex (DLPFC) is a critical node in the working memory (WM) neural circuit, established through neurophysiology, neuropsychology, and neuroimaging studies in humans and nonhuman primates. While most of the neurophysiological evidence for the role of the DLPFC in WM comes from visuospatial WM paradigms, evidence for its role in auditory WM has been suggested by the fact that large lateral prefrontal cortex lesions in nonhuman primates cause auditory discrimination deficits. Moreover, DLPFC neurons demonstrate task-related neuronal responses during auditory WM. In contrast, other studies have proposed that the ventrolateral prefrontal cortex (VLPFC) plays a pivotal role in auditory and audiovisual processing, integration, and mnemonic processing, since VLPFC neurons are responsive to complex acoustic stimuli and are robustly active during auditory WM tasks. Furthermore, inactivation of the VLPFC impairs audiovisual and auditory WM. In these inactivation studies the cortical region that was inactivated by cortical cooling included areas 12/47, 45 and 46 ventral. It is possible that inclusion of area 46 ventral may account for the auditory WM performance deficit previously observed while inactivating VLPFC so further experiments are needed.

methodsIn the present study we examined whether transient inactivation of the DLPFC, including areas 46v and 46d, and 9, in rhesus macaques would effect auditory WM. The DLPFC was inactivated by cortical cooling while two rhesus macaques performed an auditory working memory task. This was followed by permanent ibotenic acid lesions and assessment of behavioral performance post-lesion.

resultsOur experiments demonstrated that inactivation of DLPFC by cortical cooling in two macaques did not result in a significant decrease in performance of an auditory WM task. The inactivation resulted in an increase in dropped gaze events during the latter half of the task, in one subject, which could be due to a loss of attention or motivation. The ibotenic acid lesions of the DLPFC did not significantly alter performance on the auditory WM task.

conclusionsOur results showed that DLPFC transient inactivation with cortical cooling and ibotenic acid lesions did not significantly alter overall auditory working memory performance, which differs from the impairment seen when the VLPFC is inactivated. Our data suggest that the DLPFC and VLPFC may play different roles in auditory working memory.