Proceedings of The Physiological Society
University of Bristol (2005) J Physiol 567P, PC210
Processing of spatial properties of auditory and visual stimuli in the monkey prefrontal cortex
Artchakov, Denis; Linnankoski, Ilkka; Tikhonravov, Dmitri; Vuontela, Virve; Korvenoja, Antti; Carlson, Synnove;
1. Inst. Biomedicine/Physiology, University of Helsinki, Helsinki, Finland. 2. Functional Brain Imaging Unit, Medical Imaging Center, Helsinki University Central Hospital, Helsinki, Finland.
The primate dorsolateral prefrontal cortex (PFCd) is involved in visuospatial (1,2,3) and audiospatial (4) working memory. Visuospatial working memory mechanisms have been studied extensively at single cell level in the PFCd in nonhuman primates but, despite the importance of short-term memory of sound location for behavioral orientation, there are only a few studies (4) on working memory processing of auditory location. The purpose of this study was to investigate neuronal mechanisms underlying working memory processing of auditory and visual location information and possible interactions between these modalities at single cell level in the PFCd. Neuronal activity was recorded in two monkeys (Macaca mulatta) trained to perform audio- and visuospatial delayed matching to sample tasks, that required them to memorize and compare the locations (left or right) of the visual or auditory cues. For the surgery the monkeys were anaesthetized (ketamine hydrochloride 4 mg/kg i.m., pentobarbital sodium 18 mg/kg i.v.). The tasks enabled separation between neuronal activity related to encoding and maintenance of sensory information and movement preparation. A total of 325 neurons were recorded during both visual and auditory task performance. Of the neurons 287 were from the right and 38 from the left hemisphere. The activity of 111 neurons (34%) was related to some phase (cue, delay, response or reward) of the task. Twenty neurons responded during more than one phase of the task. Visually responsive, auditory responsive, and bimodal spatial neurons were found within the recorded region in the PFCd (Table 1). Of the spatially selective neurons, all delay related and most cue related neurons were modality specific and responded either during auditory or visual trials. A small number of cue related neurons were bimodal and displayed similar selectivity for spatial locations in both sensory modalities. The results indicate that processing of auditory and visual spatial information during encoding and memory maintenance involves mainly parallel cellular mechanisms, but the data also imply the existence of crossmodal mechanisms of working memory processing of auditory and visual location information in the PFCd. The maintenance of the monkeys and all procedures of the study were carried out according to the Finnish law and statutes governing animal experimentation. The Finnish Ministry of Agriculture had approved of the study and granted permission to perform it.
Where applicable, experiments conform with Society ethical requirements