Theta-Phase Dependent Neuronal Coding During Sequence Learning in Human Single Neurons

Abstract

The ability to maintain a sequence of items in short-term memory (STM) is a fundamental cognitive function. Sequential item encoding in STM has been linked to a spike-theta-phase code for sequentially organized spatial locations observed in the rodent hippocampus (phase precession). The timing of neuronal activity relative to different brain oscillations is postulated to play a key role in maintaining the sequence order. We recorded single neuron and local field potential activity in the human brain during a sequence-learning task. Spikes for two consecutive items in the sequence were phase-locked at distinct phases of the theta oscillation. Surprisingly, the order of phases in the sequence-learning task was the opposite of that observed in phase precession during navigation. These results suggest that a spike-phase code is employed in the human brain during sequence learning, but with important differences compared to the rodent spike-theta-phase-dependent coding scheme.