Advances in memory research: single-neuron recordings from the human medial temporal lobe aid our understanding of declarative memory.

PURPOSE OF REVIEW: To gain a complete understanding of how the brain functions, both in illness and good health, data from multiple levels of analysis must be integrated. Technical advances have made direct recordings of neuronal activity deep inside the human brain tractable, providing a rare glimpse into cellular processes during long-term memory formation. Recent findings using intracranial recordings in the medial temporal lobe inform current neural network models of memory, and may lead to a more comprehensive understanding of the neural basis of memory-related processes. RECENT
FINDINGS: These recordings have shown that cells in the hippocampus appear to support declarative learning by distinguishing novel and familiar stimuli via changes in firing patterns. Some cells with highly selective and invariant responses have also been described, and these responses seem to represent abstract concepts such as identity, rather than superficial perceptual features of items. Importantly, however, both selective and globally responsive cells are capable of changing their preferred stimulus depending on the conscious demands of the task.
SUMMARY: Firing patterns of human medial temporal lobe neurons indicate that cells can be both plastic and stable in terms of the information that they code; although some cells show highly selective and reproducible excitatory responses when presented with a familiar object, other cells change their receptive fields in line with changes in experience and the cognitive environment.