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.