10 September 2009
Mind-reading through the eyes
by Kate Melville
Scientists say they may be able to glean information about stored memories and past events by tracking a subject's eye movements, even when the subject is unable - or unwilling - to describe what they remember. The research, appearing in the journal Neuron, shows the relationship between activity in the hippocampus, eye movements, and both conscious and unconscious memory.
The hippocampus is a brain region that is critical for conscious recollection of past events, but the precise role of this area in memory remains controversial. According to one theory, even if explicit memory retrieval fails, the hippocampus might still support expressions of relational memory (e.g., memory for the co-occurrence of items in the context of some scene or event).
To test this theory, Drs. Deborah Hannula and Charan Ranganath, both from the Center for Neuroscience at the University of California, Davis, used fRMI to examine participants' brain activity while they attempted to remember previously studied face-scene pairings. During scanning, participants were shown a previously studied scene along with three previously studied faces and were asked to identify the face that had been paired with that scene earlier. Eye movements were also monitored during the task and provided an indirect measure of memory.
During each test, participants frequently spent more time viewing the face that had been previously paired with the scene - an eye-movement-based memory effect. What is more surprising is that hippocampal activity was closely tied to the participants' tendency to view the associated face, even when they failed to identify it. Activity in the prefrontal cortex, an area required for decision making, was sensitive to whether or not participants had responded correctly and communication between the prefrontal cortex and the hippocampus was increased during correct, but not incorrect, trials.
The findings suggest that even when people fail to recollect a past event, the hippocampus might still support an expression of memory through eye movements. Furthermore, the results suggest that even when the hippocampus is doing its job, conscious memory may depend on interactions between the hippocampus and the prefrontal cortex.
The researchers posit that it may be possible to track memory in otherwise uncooperative individuals. "It is conceivable that eye-tracking could be used to obtain information about past events from participants who are unaware or attempting to withhold information," offers Dr. Hannula. "In other words, there may be circumstances in which eye movements provide a more robust account of past events or experiences than behavioral reports alone."