Research reportInvolvement of the human medial temporal lobe in a visual discrimination task

- We examine the involvement of MTL structures in visual discrimination.
- We directly compare recognition and visual discrimination tasks in an fMRI study.
- We find significant hippocampal activation for the discrimination of pictures with high feature ambiguity, as well as for the recognition of stimuli.

Recent imaging and lesion studies suggest that the human medial temporal lobe (including the hippocampus and the perirhinal cortex), which is traditionally believed to be of central importance for memory processing, is also involved in processing and discrimination of complex visual stimuli. The aim of this study was to use functional magnetic resonance imaging in healthy subjects to further elucidate the contributions of different medial temporal lobe structures to perceptual and mnemonic processing of faces and scenes, by directly comparing the activation in a visual discrimination and a recognition task (one week after encoding). A within-subjects full factorial analysis revealed significant hippocampal activation for both discrimination and recognition task, with no differential activations for the processing of faces or scenes. No perirhinal activation was found in either of the experimental conditions. These results support a perceptual-mnemonic theory of the medial temporal lobe, while questioning a simple mapping of different functions to single structures like hippocampus and perirhinal cortex.