Investigating Selectivity for Spatial and Visual Information in Human MTL During a Spatial Association Task

Sina Mackay1, Thomas P. Reber2, Marcel Bausch1, Jan Boström3, Christian E. Elger1, Florian Mormann1

1 Dept. of Epileptology, University of Bonn
2 Faculty of Psychology, Swiss Distance University Institute, Brig, Switzerland
3 Dept. of Neurosurgery, University of Bonn

In this study we investigate cells in the human medial temporal lobe (MTL) that respond to certain stimuli or spatial positions with increased firing rates. The participants in this study were epilepsy patients with implanted depth electrodes and micro wires allowing for single unit recordings. In total we recorded from 3681 single and multi-units in 44 sessions from the 13 patients. The task consisted of multiple trial blocks in which participants were presented with a short series of images within a 3x3 grid. Each image was shown in one of the nine squares and the respective location was to be remembered. After a 15 s long distraction task, participants were asked to recall each image location. We were able to use response eliciting stimuli based on preceding screening sessions, resulting in a large number of responses to specific images by design. These types of responses were mostly found in amygdala and hippocampus, and the respective cells tended to respond to only one of the stimuli. Furthermore these responses were modulated by subsequent memory performance, with responses during successfully encoded trials being more pronounced. By contrast, responses to spatial positions were found mostly in parahippocampal cortex. Cells with spatial preferences tended to be less selective and we did not find the same modulation by subsequent memory performance.