On the neuronal activity in the human brain during visual recognition, imagery and binocular rivalry

Gabriel Kreiman

Ph.D. Thesis. Department of Biology. California Institute of Technology (defended on 08/29/2001)

How does the neuronal activity in our brains give rise to our perceptions? We recorded the electrophysiological activity of over one thousand individual neurons in the human brain during object recognition, binocular rivalry, visual imagery and sleep. Subjects were patients with intractable epilepsy implanted with depth electrodes in targets including the amygdala, entorhinal cortex and hippocampus to localize the seizure focus for potential surgical resection. This has allowed us to explore the neuronal responses during visual processing in humans at an unprecedented level of spatial and temporal resolution. We observed a high degree of selectivity in the responses to complex visual stimuli. Some units were selective to categories of pictures including faces, houses, objects, famous people and animals while others responded only to one or a few stimuli, suggesting a sparse representation of visual information in the medial temporal lobe. Most of the selective neurons modulated their responses depending on the subject's percept during flash suppression. To further explore the correlation between perception and neuronal activity we investigated the vivid images that can be voluntarily generated in our minds in the absence of concomitant visual input. Our study revealed neuronal correlates of visual imagery and supports a common substrate for the processing of visual input and recall. Since visual memory is also prominent during dreams, we investigated the neuronal responses during different stages of the sleep-wake cycle. We observed an increase in synchrony during slow wave sleep compared to the wake and rapid-eye-movement sleep states. Our results suggest that neuronal activity in the human medial temporal lobe correlates with perception, shows a strong degree of invariance to changes in the input and could be involved in processing, storing and recalling visual information.