HIPPOCAMPAL ACTIVATION DURING ENCODING OF OVERLAPPING SEQUENCES
The importance of human hippocampus in learning and memory is well known, although its role and activation patterns in specific tasks remain elusive. Sequence disambiguation, the process by which overlapping sequences are kept separate, has been proposed to underlie a wide range of memory capacities supported by the hippocampus, including episodic memory and spatial navigation. Dharshan Kumaran and Eleanor A. Maguire, from Wellcome Department of Imaging Neuroscience, Institute of Neurology, at the University College of London, used functional magnetic resonance imaging (fMRI) to explore the dynamic pattern of hippocampal activation during the encoding of faces sequences (The Dynamics of Hippocampal Activation During Encoding of Overlapping Sequences. Neuron 49, 617-629, 2006).
Kumaran & Maguire found that activation in right posterior hippocampus took place only during the encoding of overlapping sequences and robustly correlated with subject-specific behavioural index of sequence learning. Morover, hippocampal activation in response to elements in common to both sequences in the overlapping sequence pair, may be particularly important for accurate sequence encoding and retrieval.
These findings support the conclusion that the human hippocampus is involved in the earliest stage of sequence disambiguation, when memory representations are in the process of being created, and provide empirical support for contemporary computational models of hippocampal functions.