Processing of auditory and visual location information in the monkey prefrontal cortex

Abstract

Visuospatial working memory mechanisms have been studied extensively at single cell level in the dorsolateral prefrontal cortex (PFCd) in nonhuman primates. Despite the importance of short-term memory of sound location for behavioral orientation, there are only a few studies on auditory spatial working memory. The purpose of this study was to investigate neuronal mechanisms underlying working memory processing of auditory and visual location information at single cell level in the PFCd. Neuronal activity was recorded in monkeys performing a delayed matching-to-sample task (DMTS). The location of a visual or auditory stimulus was used as a memorandum. The majority of the neurons that were activated during presentation of the cue memorandum were selective either for visual or auditory spatial information. A small group of cue related bimodal neurons were sensitive to the location of the cue regardless of whether the stimulus was visual or auditory, suggesting modality independent processing of spatial information at cellular level in the PFCd. Most neurons that were activated during the delay period were modality specific, responding either during visual or auditory trials. All bimodal delay related neurons that responded during both visual and auditory trials were spatially nonselective. The results of the present study suggest that in addition to the modality specific parallel mechanism, working memory of auditory and visual space also involves modality independent processing at cellular level in the PFCd.

Distracters Impair and Create Working Memory-Related Neuronal Activity in the Prefrontal Cortex

“…The recording methods and the surgical procedures for implantation of the cylinder have been described in detail earlier (Artchakov et al 2007) and will be described in short here. Extracellular single cell activity was recorded with tungsten microelectrodes (impedances 10--20 MX, Frederick Haer & Co., Bowdoinham, ME) in the right dorsolateral PFC in 2 female rhesus monkeys (Macaca mulatta, 5.5 kg and 4.0 kg) trained to perform visual (2 monkeys) and auditory (1 monkey) spatial DMTS tasks (Fig.…”

“…The visual fixation was considered broken when the monkey's gaze moved outside of a central eye window (programmed to the size of about 2--4°), and the trial was automatically discontinued. To confirm the location of the recorded neurons in the PFC, a high-resolution structural magnetic resonance image set using a 1.5 T scanner (Siemens Sonata) was obtained from both monkeys (Artchakov et al 2007).…”

“…To calculate the onset latency of the responses to the sample cue, the spiking activity of the neurons was low-pass filtered by convolution with Gaussian distribution with r of 20 and resampling resolution at 1 ms (Artchakov et al 2007). A spike density function was created for the periods of the baseline and the sample cue (MacPherson and Aldridge 1979;Wiener and Richmond 1999), and a confidence interval (CI) of 95% from the baseline was used as a threshold for departure from the baseline.…”

“…Lesion (Jacobsen 1936;Mishkin 1957;Goldman and Rosvold 1970;Passingham 1975) and electrophysiological studies in nonhuman primates (Goldman-Rakic 1987;Fuster 1997) have indicated that the prefrontal cortex (PFC) has a central role in the performance of tasks that require short-term memory. Single PFC neurons respond to mnemonic processing of the location or content of visual (Fuster 1973;Niki 1974;Funahashi et al 1989;Wilson et al 1993;Rao et al 1997) and auditory stimuli (Bodner et al 1996;Kikuchi-Yorioka and Sawaguchi 2000;Artchakov et al 2007) and form cross-modal associations between tones and colors (Fuster et al 2000).…”

“…Single neuron activity was recorded in the dorsolateral PFC of 2 monkeys trained to perform DMTS tasks. This area was chosen because our principal aim was to investigate how randomly presented distracters affect memory-related neuronal activity, and many earlier studies have demonstrated that the area in and around the principal sulcus is involved in short-term memory processing (e.g., Fuster and Alexander 1971;Fuster 1973;Niki 1974;Goldman-Rakic 1987;Funahashi et al 1989;Carlson et al 1990Carlson et al , 1997Artchakov et al 2007). We hypothesized that taskirrelevant stimuli presented randomly during the memory maintenance period would affect the memory-related neuronal activity and impair memory task performance.…”