The hectic life of the brain
- Nature Reviews Neuroscience 3, 916 (2002); doi:10.1038/nrn999
The hectic life of the brain
Juan Carlos López
As I type these words, my phone rings. I answer the call, eventually hang up
and restart typing. Now an e-mail arrives and interrupts me again. I read the
message, send a reply and continue to write. This ability to adapt my behaviour
to satisfy current demands in the presence of competing information is known as
'cognitive control'. A recent paper by Dreher and Berman contributes to our
understanding of its neural basis by dissociating the contribution of two
different areas of the frontal lobe to cognitive control during a
The authors used a task in which subjects had to report whether a single letter
was a consonant or a vowel, lower or upper case, or before or after the letter
'm' in the alphabet. Which rule applied depended on the colour of the letter
(red, green or yellow, respectively), and the authors presented the stimuli in
blocks of three letters, one at a time, followed by a period of interruption.
For example, one block consisted of a red letter first, then a green one, with
a yellow one at the end. After a brief interruption, the next block consisted
of a sequence of red, green and red letters. For each letter, the subject had
to report its characteristics on the basis of the appropriate rule.
Dreher and Berman asked which brain regions respond when subjects switch to a
recently performed task compared with a less recent one. They measured the
response time to the last task in a triplet when it had been performed recently
(the last 'red' in a block of red, green and red letters), and compared it with
the response time to a task that had been performed less recently (the 'yellow'
in a red-green-yellow sequence). In this comparison, the response was slower
when the task had been performed recently, and there was a specific activation
of the lateral prefrontal cortex concomitant with this slower response. This
indicates that inhibition of the disengaged task is active for some time and
must be overcome to re-engage in the same task. These observations highlight
the relevance of the lateral prefrontal cortex to cognitive inhibition, and
constitute a rare dissociation between this phenomenon and memory processes.
The authors also investigated the neural basis of re-engagement in a task after
an interruption, and found activation of the anterior cingulate cortex during
this phenomenon. Behaviourally, re-engagement increased response times and
reduced error rates, consistent with the involvement of the anterior cingulate
cortex in alertness.
The neural substrates of cognitive control have been hard to pinpoint, and this
elegant dissociation and the clever experimental design should stimulate
further work in this area. Specifically, it will be important to establish how
different regions of the frontal lobe interact to generate the transitions
between cognitive operations, which we experience as a seamless continuum.
References and links
ORIGINAL RESEARCH PAPER
Dreher, J. -C. & Berman, K. F. Fractionating the neural substrate of
cognitive control processes. Proc. Natl Acad. Sci. USA 99, 14595-14600 (2002)
Miller, E. K. The prefrontal cortex and cognitive control. Nature Rev.
Neurosci. 1, 59-65 (2000)
Cognitive control: The hectic life of the brain