11 July 2011

Multi-Voxel Pattern Analysis of fMRI Reveals Brain Behind the Scenes

The research measured activity in a brain area known as the object-selective cortex (OSC) while participants were preparing to find a wide range of representational images of cars or people within briefly-displayed (100 ms) naturalistic scenes which they had not previously viewed. The subjects were first given visual cues that specified the category of objects (i.e., cars or people) to be located within the scenes. The key finding was that the cue alone – that is, even when no scene was subsequently shown – generated OSC responses determined through multivoxel pattern analysis (MVPA) that were strikingly similar to those that occurred when looking at actual examples of the cued category. Moreover, when looking at scenes, this neural activity pattern reliably predicted the subjects’ performance in detecting the cued visual target. (Unlike fMRI analysis, which focuses on individual brain voxels (volumetric pixels), MVPA enhances fMRI interpretation by identifying the information in broader patterns of brain activity.) _medXpress

New tools of brain imaging are opening new windows into the brain's basic works. The study (PNAS, doi:10.1073/pnas.1101042108) described at the link breaks new ground in understanding "top-down" mechanisms used by the brain to identify objects -- when the brain has been pre-cued as to the nature of the sought object. This type of research builds general knowledge of brain function. As the tools are refined, it will become possible to better distinguish between brain responses of different individuals. The tools will then move into a clinical setting for diagnostic and screening (learning disorders, dementia, etc.) purposes.
While the technology used was already established, and so did not present significant challenges, Peelen notes that it takes six seconds to measure a neural signature – so it was needed to overcome the way neural measurements had previously been confounded with visual activity. “We came up with a clever design in which we showed the visual cue without subsequently displaying a scene,” he adds. “Since we primary gathered data using this technique, the measured signal reflected brain activity in the absence of visual input.”

Given the brain’s ability to perceive the world using various senses, and the fact that the research relied on symbolic (rather than visually-specific) cues invoked OSC activity, Peelen says that he expects that his results would be similar with different types of symbolic cues, whether these are spoken or textual. “Indeed, if we search for something in our daily life environment, the trigger to search can come from multiple sources – that is, a thought, but also an external demand – and it is unlikely that the brain has developed different mechanisms for each of these different cues. A very interesting question is how the brain transforms a symbolic cue, such as a word, a thought, or spoken text, to a visual ‘search template’ that effectively guides visual search. Very little is known about this transformation process.” _MedXpress

Different brains are wired differently. Early brain research finds ways in which brains work alike. More refined research discovers and delineates differences. As brain imaging tools grow ever more sophisticated, the powerful drive to learn more about the human brain will run head-on into the obstinate and entrenched forces of political correctness.

Which do you think will win, ultimately?

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