Monday, October 15, 2012

The Brain on Idle

Sophisticated and highly technical functional brain imaging techniques such as fMRI and PET have revolutionized the cognitive and behavioral neurosciences.  These techniques offer a valuable non-invasive means for visualizing, localizing, and quantifying patterns of brain activity.  But a recent essay in the journal Nature focuses on what might be the important functions of the baseline brain activity that occurs when subjects in these scanners are instructed to "clear your mind".  In such instances brain activity diminishes by just a 1-5%. Some investigators believe that there is much to be learned from examining the resulting patterns in activity in the idling brain (mind). Here are some suggestions that are presented by the essays author,  Kerri Smith:
  • idling brain activity may keep essential neural pathways interconnected.
  • the activity may be necessary to prime the brain for action
  • it might be performing essential "off-line" functions related to such processes as memory consolidation.
  • it may even be that this activity may be "meaningless" - e.g., fMRI actually measures patterns of regional blood flow, not neural activity itself.
However, according to Smith, there is general agreement among most investigators that these are mere guesses (hypotheses).  What is more, it is not clear how to devise experiments to test these alternative hypotheses.

Here are some other facts that are shared in the essay:
  • patterns of intrinsic brain activity differ in distinctive ways between healthy controls and individuals with various brain disorders such as Alzheimer Disease and Autism.
  • distinctive patterns of intrinsic brain activity at any instant might predispose individuals to respond to ambiguous situations or stimuli. 
To illustrate the latter point, Smith summarizes the result of a study (Hesselmann et al., 2008) that is somewhat similar to another I learned about in a recent presentation at the College by Bill Klemm of Texas A&M.  Hesselmann et al.  compared the intrinsic patterns of brain activity in subjects just before they were presented with some classic ambiguous visual stimuli.  When presented with such stimuli subjects might perceive either the image of a face or some other image such as a vase or a reclining woman. According to Klemm what a particular individual is more likely to see initially is relatively constant from one trial to the next – the perception that an individual experiences first tend to be  reliably consistent.  Another way to say this is that is seems that their brain is prepared (possibly biased) toward perceptions of a particular nature.  And in the study by Hesselmann et al. the intrinsic pattern of activity observed in those participants who initially perceive a face was characterized by enhanced activity with a region that is known to play a role in facial perception - the fusiform face area (FFA).  The intrinsic activity of their brian just before the stimulus presentation apparently influenced their perceptions.

Are you prepared to step on your accelerator?  What hypotheses might you have for the function of intrinsic brain activity?  Do you anticipate that such intrinsic activity should resemble activity during mediation or sleep? Please share your hypotheses or ideas for how experiments might be performed to test some hypothesis presented above.

Sources Cited
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