Neuronal correlates of binocular rivalry in the human medial temporal lobe

Abstract

Firing of neurons in the human medial temporal lobe (MTL) was shown to correlate with conscious perception both using flash suppression (Kreiman et al 2002) and backward masking (Quiroga et al 2008). However, in both of these paradigms, perception was externally manipulated rather than internally driven. Thus, it remains unclear whether MTL neurons are involved in internally generating the percept, or only follow it. Here we used binocular rivalry, where perceptual switches are internally driven, in epilepsy patients implanted with depth electrodes (for clinical purpose). Based on a conventional screening paradigm, pairs of images that elicited selective responses were presented binocularly. Patients were asked to report perceptual transitions by pressing and releasing two buttons. These reports were then used to create a replay condition. We found that neurons in the MTL responded up to 1000ms before patients released the button to indicate the initiation of a perceptual switch (i.e. piecemeal period) to the cells’ preferred image. This was found both for cells that expressed selectivity by increasing or by decreasing their firing rate in response to their preferred stimulus. Even after accounting for motor reaction time, these neuronal responses are still quite early, especially considering that MTL neuronal response time is typically 300-400ms after stimulus presentation. It appears that neurons in different areas responded with different times relative to the behavioral report of the perceptual switch, with the amygdala generating some of the earliest responses. Importantly, the neuronal response was earlier in the rivalry condition as compared to the replay condition. Our results suggest that MTL neurons are not merely reflecting but likely take part in the process leading to conscious perception or to a switch in perception. Meeting abstract presented at VSS 2013