A dual role for prediction error in associative learning

Confronted with a rich sensory environment, the brain must learn statistical regularities across sensory domains to construct causal models of the world. Here, we used functional magnetic resonance imaging and dynamic causal modeling (DCM) to furnish neurophysiological evidence that statistical associations are learnt, even when task-irrelevant. Subjects performed an audio-visual target-detection task while being exposed to distractor stimuli. Unknown to them, auditory distractors predicted the presence or absence of subsequent visual distractors. We modeled incidental learning of these associations using a Rescorla--Wagner (RW) model. Activity in primary visual cortex and putamen reflected learning-dependent surprise: these areas responded progressively more to unpredicted, and progressively less to predicted visual stimuli. Critically, this prediction-error response was observed even when the absence of a visual stimulus was surprising. We investigated the underlying mechanism by embedding the RW model into a DCM to show that auditory to visual connectivity changed significantly over time as a function of prediction error. Thus, consistent with predictive coding models of perception, associative learning is mediated by prediction-error dependent changes in connectivity. These results posit a dual role for prediction-error in encoding surprise and driving associative plasticity

Frequency of gamma activity is modulated by motivation in the auditory cortex of cat

Repetitive acoustic stimuli elicit steady-state response (SSR) in the gamma-band both in humans and in mammals. Our aim was to investigate changes of the spontaneous gamma activity and the SSR in the auditory cortex of cats in the background of an instrumental conditioning situation. Epidural electrodes were chronically implanted above the auditory neocortex. The presentation rate of the clicks varied between 20 and 65/s. Spontaneous EEG and SSR were collected in three behavioral states: in an indifferent environment, in the instrumental cage while the cat was waiting for the light CS, and when she stepped on the pedal and was waiting for the meat reward. Using different repetition rate clicks we determined which stimulus rate elicited the largest SSR in these three situations. In quiet animal the highest SSR appeared at 28-30/s. Before and during the CS the optimal stimulus rate shifted to 32-38/s. The frequency of the spontaneous gamma activity changed in parallel way depending on the situation. We conclude that both the SSR and the spontaneous gamma activity reflect resonant activity of the same neuronal circuit of the auditory cortex, and it is modulated by the motivational state of the animal

Nonhuman primate event-related potentials indexing covert shifts of attention

A half-century's worth of research has established the existence of numerous event-related potential components measuring different cognitive operations in humans including the selection of stimuli by covert attention mechanisms. Surprisingly, it is unknown whether nonhuman primates exhibit homologous electrophysiological signatures of selective visual processing while viewing complex scenes. We used an electrophysiological technique with macaque monkeys analogous to procedures for recording scalp event-related potentials from humans and found that monkeys exhibit short-latency visual components sensitive to sensory processing demands and lateralizations related to shifting of covert attention similar to the human N2pc component. These findings begin to bridge the gap between the disparate literatures by using electrophysiological measurements to study the deployment of visual attention in the brains of humans and nonhuman primates