prefrontal cortex

is the area of the brain at the very front of the frontal lobes. It is involved in "executive functions", such as working memory, decision-making, planning and judgment. Prefrontal regions appear to be particularly sensitive to the effects of aging. It is thought that the reduced ability to recall the context of memories that occurs with advancing age, is evidence that the prefrontal cortex is also critical for context processing - a process involved in many cognitive functions. A recent study has also revealed that emotional stimuli and attentional functions are integrated in a specific part of the prefrontal cortex - the anterior cingulate (located between the right and left halves).

Cognitive recovery after brain damage more complex than realized

January, 2011

Two new studies show us that recovery after brain damage is not as simple as one region ‘taking over’ for another, and that some regions are more easily helped than others.

When stroke or brain injury damages a part of the brain controlling movement or sensation or language, other parts of the brain can learn to compensate for this damage. It’s been thought that this is a case of one region taking over the lost function. Two new studies show us the story is not so simple, and help us understand the limits of this plasticity.

In the first study, six stroke patients who have lost partial function in their prefrontal cortex, and six controls, were briefly shown a series of pictures to test the ability to remember images for a brief time (visual working memory) while electrodes recorded their EEGs. When the images were shown to the eye connected to the damaged hemisphere, the intact prefrontal cortex (that is, the one not in the hemisphere directly receiving that visual input) responded within 300 to 600 milliseconds.

Visual working memory involves a network of brain regions, of which the prefrontal cortex is one important element, and the basal ganglia, deep within the brain, are another. In the second study, the researchers extended the experiment to patients with damage not only to the prefrontal cortex, but also to the basal ganglia. Those with basal ganglia damage had problems with visual working memory no matter which part of the visual field was shown the image.

In other words, basal ganglia lesions caused a more broad network deficit, while prefrontal cortex lesions resulted in a more limited, and recoverable, deficit. The findings help us understand the different roles these brain regions play in attention, and emphasize how memory and attention are held in networks. They also show us that the plasticity compensating for brain damage is more dynamic and flexible than we realized, with intact regions stepping in on a case by case basis, very quickly, but only when the usual region fails.

Reference: 

[2034] Voytek, B., Davis M., Yago E., Barcel F., Vogel E. K., & Knight R. T.
(2010).  Dynamic Neuroplasticity after Human Prefrontal Cortex Damage.
Neuron. 68(3), 401 - 408.

[2033] Voytek, B., & Knight R. T.
(2010).  Prefrontal cortex and basal ganglia contributions to visual working memory.
Proceedings of the National Academy of Sciences. 107(42), 18167 - 18172.

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Children with autism have distinctive patterns of brain activity

December, 2010

An imaging study has found three different brain signatures discriminating children with autistic spectrum disorders, siblings of children with ASD, and other typically-developing children.

Last month I reported on a finding that toddlers with autism spectrum disorder showed a strong preference for looking at moving shapes rather than active people. This lower interest in people is supported by a new imaging study involving 62 children aged 4-17, of whom 25 were diagnosed with autistic spectrum disorder and 20 were siblings of children with ASD.

In the study, participants were shown point-light displays (videos created by placing lights on the major joints of a person and filming them moving in the dark). Those with ASD showed reduced activity in specific regions (right amygdala, ventromedial prefrontal cortex, right posterior superior temporal sulcus, left ventrolateral prefrontal cortex, and the fusiform gyri) when they were watching a point-light display of biological motion compared with a display of moving dots. These same regions have also been implicated in previous research with adults with ASD.

Moreover, the severity of social deficits correlated with degrees of activity in the right pSTS specifically. More surprisingly, other brain regions (left dorsolateral prefrontal cortex, right inferior temporal gyrus, and a different part of the fusiform gyri) showed reduced activity in both the siblings group and the ASD group compared to controls. The sibling group also showed signs of compensatory activity, with some regions (right posterior temporal sulcus and a different part of the ventromedial prefrontal cortex) working harder than normal.

The implications of this will be somewhat controversial, and more research will be needed to verify these findings.

Reference: 

[1987] Kaiser, M. D., Hudac C. M., Shultz S., Lee S. M., Cheung C., Berken A. M., et al.
(2010).  Neural signatures of autism.
Proceedings of the National Academy of Sciences.

Full text available at http://www.pnas.org/content/early/2010/11/05/1010412107.full.pdf+html

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Women's brains grow after giving birth

November, 2010

A small study indicates that nurturing mothers and increased reward centers in the brain go hand-in-hand — although the jury’s still out on which comes first.

The issue of “mommy brain” is a complex one. Inconsistent research results make it clear that there is no simple answer to the question of whether or not pregnancy and infant care change women’s brains. But a new study adds to the picture.

Brain scans of 19 women two to four weeks and three to four months after they gave birth showed that grey matter volume increased by a small but significant amount in the midbrain (amygdala, substantia nigra, hypothalamus), prefrontal cortex, and parietal lobe. These areas are involved in motivation and reward, emotion regulation, planning, and sensory perception.

Mothers who were most enthusiastic about their babies were significantly more likely to show this increase in the midbrain regions. The authors speculated that the “maternal instinct” might be less of an instinctive response and more of a result of active brain building. Interestingly, while the brain’s reward regions don’t usually change as a result of learning, one experience that does have this effect is that of addiction.

While the reasons may have to do with genes, personality traits, infant behavior, or present circumstances, previous research has found that mothers who had more nurturing in their childhood had more grey matter in those brain regions involved in empathy and reading faces, which also correlated with the degree of activation in those regions when their baby cried.

A larger study is of course needed to confirm these findings.

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Individual differences in ability to gauge your own accuracy

October, 2010

Differences in the size and connectivity of a region in the prefrontal cortex underlie how accurate people are in judging their own performance.

Metamemory or metacognition — your ability to monitor your own cognitive processes — is central to efficient and effective learning. Research has also shown that, although we customarily have more faith in person’s judgment the more confident they are in it, a person’s accuracy and their confidence in their accuracy are two quite separate things (which is not to say it’s not a useful heuristic; just that it’s far from infallible). A new study involving 32 participants has looked at individual differences in judging personal accuracy when assessing a geometric image, comparing these differences to differences in the brain.

The perceptual test used simple stimuli, and each one was customized to the individual's level of skill in order to achieve a score of 71%. In keeping with previous research, there was considerable variation in the participants’ accuracy in assessing their own responses. But the intriguing result was that these differences were reflected in differences in the volume of gray matter in the right anterior prefrontal cortex. Moreover, those who were better at judging their own performance not only had more neurons in that region, but also tended to have denser connections between the region and the white matter connected to it. The anterior prefrontal cortex is associated with various executive functions, and seems to be more developed in humans compared to other animals.

The finding should not be taken to indicate a genetic basis for metacognitive ability. The finding implies nothing about whether the physical differences are innate or achieved by training and experience. However it seems likely that, like most skills and abilities, a lot of it is training.

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Change in our understanding of memory development

September, 2010

Children’s slowly developing memory for past events may not be due to the slow development of the prefrontal cortex, as was thought, but to changes in the hippocampus.

Children’s ability to remember past events improves as they get older. This has been thought by many to be due to the slow development of the prefrontal cortex. But now brain scans from 60 children (8-year-olds, 10- to 11-year-olds, and 14-year-olds) and 20 young adults have revealed marked developmental differences in the activity of the mediotemporal lobe.

The study involved the participants looking at a series of pictures (while in the scanner), and answering a different question about the image, depending on whether it was drawn in red or green ink. Later they were shown the pictures again, in black ink and mixed with new ones. They were asked whether they had seen them before and whether they had been red or green.

While the adolescents and adults selectively engaged regions of the hippocampus and posterior parahippocampal gyrus to recall event details, the younger children did not, with the 8-year-olds indiscriminately using these regions for both detail recollection and item recognition, and the 10- to 11-year-olds showing inconsistent activation. It seems that the hippocampus and posterior parahippocampal gyrus become increasingly specialized for remembering events, and these changes may partly account for long-term memory improvements during childhood.

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