(Medical Xpress) -- Rather than being a passive state, perception is an active process fueled by predictions and expectations about our environment. In the latter case, memory must be a fundamental component in the way our brain generates these precursors to the perceptual experience – but how the brain integrates long-term memory with perception has not been determined. Recently, however, researchers in the Department of Experimental Psychology at the University of Oxford, by devising a method for integrating memory and attention, showed how LTM optimizes perception by varying brain states associated with anticipation of spatial localization in the visual field. The scientists also used fMRI to articulate a neural network involving a number of cortical areas likely to be active in the predictive use of memory in the visual cortex.
Lead researcher Mark G. Stokes, working with Kathryn Atherton, Eva Zita Patai, and Anna Christina Nobre, explains that to study how memory guides attention, it was first necessary to train each participant of the experiment to remember a large number of associations that can then be used to guide attention. “In this study,” Stokes tells Medical Xpress, “we exploited the brain’s inherent ability to remember specific spatial locations within natural scenes. Despite the enormous visual complexity in such scenes, the brain is extremely adept at processing this kind of information, and can store essential details in long-term memory with little apparent effort. This ability is an ideal route for us to experimentally manipulate the contents of long-term memory to test the effects of attention on visual performance, and explore the underlying brain basis with EEG and fMRI.”
To accomplish this, says Stokes, the key methodological development in their research was to specifically measure how long-term memories modulate preparatory brain activity. “For the fMRI experiment, this involved a technique called event-related fMRI, which allows us to separate statistically the brain response to distinct cognitive events. Incorporating high-temporal resolution EEG was also a key innovation in this research, providing a more direct real-time measure of memory related changes in preparatory brain activity.”
The next step in the team’s research was to determine how an integrated circuit of attention and memory related brain areas – the frontoparietal cortex, and hippocampus, respectively – are coordinated for memory-guided attention. “So far we’ve demonstrated which brain areas are active,” Stokes notes, “but more detailed imaging data could also tell us how these areas communicate. Moreover, disruption methods like Transcranial Magnetic Stimulation can pinpoint which nodes of the frontoparietal network are necessary for memory guided attention.”
Commenting on how their findings might impact other areas, Stokes points out that integrating high-spatial resolution fMRI and high-temporal resolution EEG would be a powerful approach for a range of cognitive neuroscience applications. It also might be possible, Stokes agrees, to transition to a completely in silico model based on optogenetics-derived data.
More information: Long-term memory prepares neural activity for perception, PNAS, Published online before print November 22, 2011, doi: 10.1073/pnas.1108555108
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