Probabilistic Decision Making by Slow Reverberation in Cortical Circuits (original) (raw)

motor output of the animal's decision). Indeed, Shadlen and Newsome found that activity of LIP cells signals the monkey's perceptual choice in both correct and error trials (Shadlen and Newsome, 1996, 2001). Activity of Summary LIP neurons showed a slow ramping time course during stimulus viewing and persisted throughout a delay be-Recent physiological studies of alert primates have revealed cortical neural correlates of key steps in a tween the stimulus and the monkey's saccadic response. LIP neurons do not simply reflect sensory sig-perceptual decision-making process. To elucidate synaptic mechanisms of decision making, I investi-nals, because their activity is correlated with what the monkey decides, when the decision varies from trial gated a biophysically realistic cortical network model for a visual discrimination experiment. In the model, to trial even at zero stimulus coherence. LIP neuronal activity cannot be purely a motor signal either, since its slow recurrent excitation and feedback inhibition produce attractor dynamics that amplify the difference time course varies systematically with the motion signal strength (the quality of the sensory information), even between conflicting inputs and generates a binary choice. The model is shown to account for salient though the saccadic motor output is basically the same (Shadlen and Newsome, 2001). characteristics of the observed decision-correlated neural activity, as well as the animal's psychometric Similar decision-correlated neural activity has been reported in prefrontal cortex during the same visual mo-function and reaction times. These results suggest that recurrent excitation mediated by NMDA receptors tion discrimination task (Kim and Shadlen, 1999) and in medial premotor cortex during a vibrotactile discrimina-provides a candidate cellular mechanism for the slow time integration of sensory stimuli and the formation of tion task (Romo et al., 1997; Herná ndez et al., 2002). Assuming that the neural activity signaling decisions is categorical choices in a decision-making neocortical network. generated within a cortical circuit, an intriguing question is: what are the basic cellular and synaptic mechanisms of a decision-making circuit? A clue comes from the