Ranulfo Romo : Where and how in the cerebral cortex do single neurons process more than one sensory modality during perceptual judgments?

Instituto de Fisiología Celular-Neurociencias, Universidad Nacional Autónoma de México & El Colegio Nacional,  Mexico City

 

Recent studies have reported that sensory cortices process more than one sensory modality, challenging the long-lasting concept that they process only one. However, both the identity of these multi-modal responses and whether they contribute to perceptual judgments are unclear. With my colleagues I recorded from single neurons in somatosensory cortices and primary auditory cortex while trained monkeys discriminated, on interleaved trials, either between two tactile flutter stimuli or between two acoustic flutter stimuli, and in cross modal trials. We found few neurons in these sensory cortices that responded to stimuli that are not of their principal modality during these tasks. The identity of the stimulus could only be decoded from responses of their principal sensory modality during the stimulation periods and not during the processing steps that link sensation to decision making. These results suggest that multimodal encoding and perceptual judgments in these tasks occur outside the sensory cortices. New experiments using the same discrimination sets described above showed that single neurons from the frontal lobe cortices have the capacity to encode the tactile and acoustic flutter stimuli during the stimulation periods, working memory and decision periods of these tasks. Furthermore, the single neurons from the frontal lobe encode in their activities the quantities of either tactile or acoustic stimuli and covary with the perceptual judgments in these two tasks.