Time Hierarchy in the Cerebral Cortex

Tommi Raij, Radiology, Harvard Medical School

Temporal integration presents a key challenge to information processing in the human brain. Fleeting sensory information must be incorporated with perceptual and cognitive processes unfolding over considerably longer timescales. This talk attempts to reveal the large-scale functional organization of the brain supporting these functions. Our recordings show that durations of neuronal activation traces are shortest in primary sensory cortices and systematically increase towards association cortices. Further, in some association areas the neuronal activation trace remains strong relatively long, thus sustaining and facilitating integration of exact stimulus features over time, whereas in other areas the trace quickly looses most of its energy but is then preserved in a weaker form, plausibly supporting emergence of abstract representations. These findings offer a simple mechanistic explanation for cortical functional hierarchy and give new insight to neural underpinnings of temporal integration, time perception, and memory.