Wednesday, December 13, 2006

Mental time clock - fewer brain areas involved?

In prior posts re: mental/interval time-keeping, I have drawn on key neuroscience research articles regarding the potential brain areas/functions involved in the brain's master clock (this information was summarized in the "Interactive Metronome: Whats happening under the hood" on-line PPT slide show available on the right side of this blog) . This week I ran across a new fMRI study that questions the number and breadth of involvement of some of these key areas of the brain (viz., cerebullum, basal ganglia, frontal-striatal loop, dorsolateral prefrontal cortex, parietal lobe) in mental time-keeping. Below is the article reference and abstract. I believe the article speaks for itself.

As with all science, this is one more bit of information that needs to be added to the extant research knowledge base. The preponderance of research to date suggests the involvement of the areas summarized above, but this new study needs to examined (and hopefully replicated) so that possible adjustments to current thinking can be modified as needed.

I've also placed this article in the the "key research articles" section of this blog.

Livesey, A., Wall, M. Smith, A. (2007). Time perception: Manipulation of task difficulty dissociates clock functions from other cognitive demands Neuropsychologia,45,321–331. (click here to view)

Abstract (italics added by blogmaster)
  • Previous studies suggest the involvement in timing functions of a surprisingly extensive network of human brain regions. But it is likely that while some of these regions play a fundamental role in timing, others are activated by associated task demands such as memory and decisionmaking. In two experiments, time perception (duration discrimination) was studied under two conditions of task difficulty and neural activation was compared using fMRI. Brain activation during duration discrimination was contrasted with activation evoked in a control condition (colour discrimination) that used identical stimuli. In the first experiment, the control task was slightly easier than the time task. Multiple brain areas were activated, in line with previous studies. These included the prefrontal cortex, cerebellum, inferior parietal lobule and striatum. In the second experiment, the control task was made more difficult than the time task. Much of the differential time-related activity seen in the first experiment disappeared and in some regions (inferior parietal cortex, pre-SMA and parts of prefrontal cortex) it reversed in polarity. This suggests that such activity is not specifically concerned with timing functions, but reflects the relative cognitive demands of the two tasks. However, three areas of time-related activation survived the task-difficulty manipulation: (i) a small region at the confluence of the inferior frontal gyrus and the anterior insula, bilaterally, (ii) a small portion of the left supramarginal gyrus and (iii) the putamen. We argue that the extent of the timing “network” has been significantly over-estimated in the past and that only these three relatively small regions can safely be regarded as being directly concerned with duration judgements.
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