8/03/2006

Functionally Dissociating Right and Left dlPFC

Shallice's chapter of Attention & Perfomance XXI focuses on two of the functions that are neccessary for cognitive flexibility: the production of procedures that can be used to attain a goal, and the "error checking" that must be done to ensure that the produced actions are helping to attain the goal. He argues that these computations are primarily subserved by the left and right dorsolateral prefrontal cortex (DLPFC), respectively, and that together they fit well with the ways prefrontal cortex has been described (e.g., as involved in the on-line monitoring, maintenance, and manipulation of recent information).

Shallice reviews several studies that seem to support this hypothesis, such as:

1) Jahanshahi et al's 1998 study showing that repetitive transcranial magnetic stimulation (TMS) to the left DLPFC more strongly disrupted random number generation than TMS to the right DLPFC, suggesting that left DLPFC is involved in random number generation process itself (though it seems to me that this particular result could just as well implicate lDLPFC as an error checker)

2) right but not left DLPFC damage resulting in twice as many perseverative responses in a free-recall task, thus suggesting that rDLPFC is normally involved in "editing" or "checking" processes (Stuss et al 1994);

3) Decreased accuracy in memory judgments is accompanied by increased rDLPFC activity, this implicating rDLPFC in "error checking" - albeit unsuccessfully in these studies (Henson et al., 1999 & Eldridge et al 2000);

4) Increased rDLPFC (but not lDLPFC) activity with increasing proactive intereference (Henson et al 2002)

5) An EEG wave appears directly centered on rDLPFC electrodes, at around 1 second after stimulus presentation, thus fitting the "temporal profile" of a region responsible for error checking (Wilding & Rugg 1996)

6) repetitive TMS over rPFC during retrieval or over lPFC during encoding, in a visual recognition memory task, significantly decreased recognition accuracy; however, only rPFC TMS resulted in a significant lowering of the response criterion from that found in a baseline "sham TMS" condition (Rossi et al 2001)

7) In a visuospatial version of the Wisconsin Card Sort (the Brixton Spatial Rule Attainment task) where subjects must determine the rule governing the varying location of blue dots on a series of cards, and must ignore the rule governing the varying location of red dots on the same cards, patients with right lateral prefrontal but not left lateral prefrontal showed a tendency to make perseverative errors (Reberberi et al, 2004).

It should be noted that it is difficult to rule out an alternate explanation of how/when rDLPFC is recruited for tasks: perhaps rDLPFC is simply involved when cognitive effort is increased. Of course, this may be a complementary (but in my opinion, less concrete) form of the "error checking" hypothesis.

On the other hand, I have reviewed previous studies with findings that are compatible with this view. For example, the recent Weissman et al. paper in Nature Neuroscience showed rPFC and ACC reductions during lapses of attention. Earlier this week I wrote about another compatible finding, this time from Neuropsychologia, in which right (ventro-) lateral regions PFC were activated selectively by negative (not positive) feedback.

Related Posts:

Imaging Lapses of Attention

Reversing Time: Temporal Illusions
Developmental Change in the Neural Mechanisms of Risk and Feedback Perception

2 Comments:

Blogger YsGuy said...

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8/05/2006 04:27:00 AM  
Blogger YsGuy said...

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8/05/2006 04:32:00 AM  

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