How does the brain encode courage? This is the question that Israeli researchers, headed by Uri Nili from the Weizmann Institutide of Science, seek to answer. Their research, published in Neuron under the title Fear Thou Not: Activity of Frontal and Temporal Circuits in Moments of Real Life Courage, identifies specific brain regions whose activity correlates with the behavioral expression of courage. Defining courage as the “performance of voluntary action opposed to that promoted by ongoing fear”, Nili and colleagues used functional MRI to look at brain activity during a behavioral task requiring the expression of courage.
The Experimental Setup and Protocol, with Illustrative behavior of a Participant (depicting position of the object relative to the participant, starting from most distant at 0)
Participants were placed in an fMRI machine, and a live corn snake was place on a trolley that extended from the end of the exam room to next to the subjects head within the scanner. The trolley could be moved either towards or away from participants heads in a step-wise manner. Participants (both those who feared snakes and those who were used to handling snakes) were given control of the location of the trolley, and repeatedly asked to choose whether to advance or retreat the snake, the overall goal being to bring the snake as close to their heads as possible.
The researchers imaged the brains of the participants as they made their choices, and identified differences between brain activity when the subjects overcame their fear (moved the snake closer), and when they succumbed to it (moved the snake away). Specifically, two brain regions were found to show activity correlating with overcoming fear, the subgenual anterior cingulate cortex (sgACC) and the right temporal pole (rTP).
Of particular interest was the activity of the sgACC, which showed positive correlation with choosing to bring the snake closer. In trials when fear was overcome, sgACC activity increased during the delay period between presentation of the snakes location and the cue to make the choice, with activity remaining elevated until the button to advance the snake was pressed. In trials where subjects succumbed to their fear, the sgACC activity declined rapidly after the snakes location was presented. The sgACC therefore appears to display on-line activation correlating with the decision to overcome or succumb to fear. Furthermore, greater sgACC activity occurred in trials where greater levels of fear were overcome. From these correlations, as well as other data described in the study, the researchers concluded that activity in the sgACC reflects the effort necessary to overcome fear.
Average percent BOLD signal change in the sgACC (left panel) and rTP (right panel) ROIs of the Fearful Non-retreaters and Fearless groups in Advance choices of the Snake condition. Black and gray heavy dotted lines represent the choice button presses of the Fearless and Fearful Non-retreaters groups, respectively.
Of note to fear conditioning aficionados, the sgACC is encompassed by the ventromedial prefrontal cortex, a region previously implicated in retrieval of inhibitory associations in studies of fear conditioning, although as the authors note, previous studies of vmPRC found no on-line role for the region during acquisition of extinction of fear conditioning, a finding potentially at odds with the on-line role for sgACC described in this study.
Nevertheless, given previous knowledge regarding the connectivity of the sgACC, as well as the activity of multiple other brain regions during the snake-movement task, Nili et al propose a model of courage whereby the sgACC inhibits the amygdala, reducing autonomic arousal and promoting subjects to choose action at odds with that prompted by their fear of snakes. The authors round out their paper by suggesting that manipulating sgACC activity may be a potential intervention for disorders involving an inability to overcome fear, and by pointing out place of their research in a field seeking to understand how the brain shirts between internal representations to select a context-specific behavioral outcome.
For a more thorough description of the paper, watch the video abstract, available courtesy of Neuron, which features the researchers discussing their research. Additionally, the paper is available online:
doi:10.1016/j.neuron.2010.06.009
Thursday, July 22, 2010
Stanford Neuroblog - Your Courageous Brain
I stumbled upon a cool new blog from Stanford University - the Stanford Neuroblog. Geeky science and neuroscience - good stuff. Here is a recent post.
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