Friday, December 30, 2005

Anterior cingulate cortex


The structure of today is the anterior cingulate cortex (ACC). Two new studies jointly illuminate the function played by this intriguing part of the brain. In many imaging studies the ACC lights up in connection with cognitive processing, especially when something goes wrong. Some researchers have speculated that the ACC may work as a cognitive error-detection device. Other studies implicate the ACC in emotional processing (and, traditionally, the ACC has been grouped anatomically as part of the limbic system). So, what is it, cognition or emotion?

In a forthcoming paper in Brain and Cognition, Ray Dolan, Hugo Critchley and their colleagues at FIL in London test two patients with damage to the medial part of the prefrontal cortex (including ACC) on a number of cognitive tasks. They conclude (citing the abstract) that

both patients showed intact intellectual, memory, and language abilities. No clear-cut abnormalities were noted in visuoperceptual functions. Speed of information processing was mildly reduced only in Patient 2 (bilateral ACC lesion). The patients demonstrated weak or impaired performance only on selective executive function tests. Performance on anterior attention tasks was satisfactory.

This suggests, they say, that

our findings are inconsistent with anterior attention theories of ACC function based on neuroimaging findings. We propose that the data may imply that the ACC does not have a central role in cognition. We speculate that our findings may be compatible with the view that the ACC integrates cognitive processing with autonomic functioning to guide behaviour.

As it so happens, another new study by scientists at Stanford and Harvard, reported two weeks ago in PNAS, backs up this conclusion. In this study, subjects used real-time fMRI to modulate feelings of pain by learning to control activity in the rostal part of the ACC. This finding is really quite astonishing, I think! As the authors remark in the abstract to their paper

When subjects deliberately induced increases or decreases in rACC fMRI activation, there was a corresponding change in the perception of pain caused by an applied noxious thermal stimulus. Control experiments demonstrated that this effect was not observed after similar training conducted without rtfMRI information, or using rtfMRI information derived from a different brain region, or sham rtfMRI information derived previously from a different subject. Chronic pain patients were also trained to control activation in rACC and reported decreases in the ongoing level of chronic pain after training. These findings show that individuals can gain voluntary control over activation in a specific brain region given appropriate training, that voluntary control over activation in rACC leads to control over pain perception, and that these effects were powerful enough to impact severe, chronic clinical pain.

The over-all conclusion, thus, appears to be that the ACC do have something to do with the control of behaviour, but mostly with emotional behaviour. Why does it then pop up in so many imaging experiments on cognition? One possible answer could be that the ACC is the neurocognitive seat for integrating emotional responses to some activity or perception with the sequencing of cognitive behaviour. Further research will hopefully tell.


References

Baird, A. et al. (in press): Cognitive functioning after medial frontal lobe damage including the anterior cingulate cortex: A preliminary investigation. To appear in Brain and Cognition.

deCharms, R.C. et al. (2005): Control over brain activation and pain learned by using real-time functional MRI. PNAS 102: 18626-18631.

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