The Role of Anterior Nuclei of the Thalamus: a Subcortical Gate in Memory Processing. An Intracerebral Recording Study.

Abstract Objective To study the involvement of the posterior medial cortex (PMC), the anterior nuclei of the thalamus (ANT), and the hippocampus in the processes of encoding and recognition during visual and verbal (auditory) memory tasks. Methods We studied intracerebral recordings in epilepsy-surgery candidates using depth electrodes implanted in the retrosplenial cingulate, precuneus, cuneus, lingual gyrus, and hippocampus and in patients with pharmacoresistent epilepsy who underwent deep brain stimulation (DBS) of the ANT with depth electrodes implanted bilaterally in the ANT. We recorded the event-related potentials (ERPs) evoked by visual and verbal memory encoding-recognition tasks. Results In the hippocampus, ERPs were elicited in the encoding and recognition phases in both visual and verbal modalities. In the PMC and ANT, ERPs were recorded in both the encoding and recognition visual tasks; in the verbal modality, they were recorded in the recognition task, but not in the encoding task. In the visual and verbal recognition tasks, the ERPs (P300-like potentials) in the ANT preceded the P300-like potentials in the hippocampus. Conclusions The PMC and the ANT are modality dependent in memory processing. ERPs are elicited by memory recognition, but they are not elicited by verbal encoding memory processing in the PMC and ANT. The PMC appears to be involved in higher-order top-down cognitive activities as well as in more basic, rather bottom-up activities. The ANT is a structure in the memory pathway that processes memory information before the hippocampus. We suggest that the ANT has a specific role in memory processes, especially memory recognition, and that memory disturbance should be considered in patients with ANT-DBS and in patients with ANT and PMC lesions. ANT is well positioned to serve as a subcortical gate for memory processing in cortical structures. Key words: event-related potentials (ERPs), P300 like potentials, memory, posterior medial cortex (PMC), hippocampus, stereoelectroencephalography (SEEG), deep brain stimulation (DBS), anterior nuclei of the thalamus (ANT)