Memory-selective neurons in human medial temporal lobe and medial frontal cortex can be modulated by the decision criterion during recognition memory

Poster Session C - Sunday, April 14, 2024, 5:00 – 7:00 pm EDT, Sheraton Hall ABC

Evan Layher^1,2 (layher@psych.ucsb.edu), Michael B. Miller², Adam N. Mamelak¹, Ueli Rutishauser¹; ¹Cedars-Sinai Medical Center, ²University of California, Santa Barbara

According to Signal Detection Theory, a recognition memory judgment consists of determining whether the familiarity strength elicited by an item exceeds the decision criterion for classifying it as previously studied (old) or novel (new). While many experiments have investigated the neural mechanisms underlying the memory component of recognition tests, much less work has explored the neural underpinnings of the decision criterion. Recent fMRI findings revealed that widespread frontoparietal activity in old versus new response contrasts is greatly affected by changes in criterion placement regardless of task difficulty (Layher et al., 2023). To expand on these findings, we administered a recognition memory task that included manipulations of criterion placement and task difficulty in seven epilepsy patients with depth-electrode implants. We obtained single-unit recordings from these patients in the amygdala, hippocampus, anterior cingulate cortex, supplementary motor area, ventromedial prefrontal cortex, and fusiform face area. Across all regions, we isolated 688 neurons and identified 80 memory-selective neurons that showed significantly different firing rates between correct old and new responses during the test stimulus presentation period. A support vector machine (SVM) decoding classifier determined if the firing rates of the 80 identified memory-selective neurons were modulated by manipulations of criterion placement and/or task difficulty. The SVM classifier successfully decoded response type (85%, p < .001) and criterion condition (68%, p < .001), but failed to differentiate the task difficulty level (52%, p = .30). These preliminary results suggest that memory-selective neurons in the recorded regions can encode decisional information related to criterion placement.

Topic Area: LONG-TERM MEMORY: Episodic