Monday, September 03, 2007

The topography of fear

Mobbs and colleagues have devised an ingenious experiment to evaluate how different neural circuits in the human brain are engaged by distal and proximal threats. From the review of this work by Maren:
Mobbs and colleagues developed a computerized virtual maze in which subjects are chased and potentially captured by an "intelligent" predator. During the task, which was conducted during high-resolution functional magnetic resonance imaging (fMRI) of cerebral blood flow (which reflects neuronal activity), subjects manipulated a keyboard in an attempt to evade the predator. Although the virtual predator appeared quite innocuous (it was a small red circle), it could cause pain (low- or high-intensity electric shock to the hand) if escape was unsuccessful. Brain activation in response to the predatory threat was assessed relative to yoked trials in which subjects mimicked the trajectories of former chases, but without a predator or the threat of an electric shock....the prefrontal cortex and lateral amygdala were strongly activated when the level of threat was low, and this activation shifted to the central amygdala and periaqueductal gray when the threat level was high.

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