Ketamine changes the neural representation of object recognition in early visual cortex.

Abstract

 

What does recognition of an object do to its representation in the brain? Previous research demonstrated that recognition alters the spatial patterns of fMRI activation even in early visual cortex (Hsieh et al. 2010). This process is thought to depend on feedback from higher-level areas to early visual areas. In turn, feedback activity is suggested to rely on the NMDA-receptor. To investigate the role of feedback in the effect of recognition, we administered Ketamine, an NMDA-receptor antagonist, or a placebo to participants. Participants viewed Mooney images that were initially unrecognizable and later recognizable and grayscale photo versions of the same images. We used representational dissimilarity matrixes (RDM) to investigate how the spatial patterns of fMRI activation changed with recognition. Preliminary data suggests that when the Mooney images are unrecognizable their representation pattern is more similar compared to when the Mooney images are recognized. In other words: from the neural perspective unrecognizable Mooney images all ‘look the same’, and different neural representations only arise upon recognition. Our data further indicate that the neural patterns of recognized Mooney images more strongly resemble neural patterns of the photographic images than of same Mooney images when not recognized. This effect was observed both in early visual areas and in object related areas. Ketamine reduced these effects of recognition in early visual areas. The representation pattern of the recognized Mooney images remained more similar and as a result resembled the RDM of the unrecognized Mooney images more than with placebo. This suggests that reduction of feedback by Ketamine counteracts the effect of object recognition in early visual areas, or even that feedback is necessary for recognition to occur.

 

Meeting abstract presented at VSS 2013