How to not do something

The internet is full of helpful people offering their advice to others through how-to guides. Most involve important daily problems, such as ‘how to rip paper’, ‘how to take a shower’, and ‘how to hide an erection’. I, as an equally nice person, will offer my own guide. I will teach you how to inhibit something you’re about to do, explained in patterns of neural activity.

We’ve known from lesion studies that three regions are important in the inhibition of actions and that lesions to those areas impair one’s ability to inhibit actions. Those regions are: preSMA, inferior frontal gyrus (IFG), and subthalamic nucleus (STN; Aron et al., 2003; Eagle et al., 2008; Nachev et al.; 2007). What we didn’t know though was how exactly those areas interact and allow humans to inhibit actions. A recent paper by Rae et al. (2015) has found a possible explanation.

In one sentence, Rae et al. found that IFG modulates the connection between preSMA and STN. To put this into context: M1 is the brain area that sends motor commands to the muscles. STN can inhibit M1 though if we realise that we don’t want to make a movement. PreSMA can increase the activity in STN, and IFG can increase this connection between preSMA and STN. Put simply, STN acts as a kind of brake for M1. This brake can be released by the preSMA and can be accelerated if IFG increases the connectivity between preSMA and STN. So if we want to inhibit an action extra fast, we should additionally employ IFG.

What makes this study particularly cool is the use of different methods. First they used fMRI in combination with dynamical causal modelling to find out how the different brain regions interact to inhibit an action. Then, they managed to cross-validate their own findings by finding that the white matter structure in the tract between preSMA and STN correlated with the effective connectivity of that pathway. The mean diffusivity between those two regions also predicted inhibition performance in the experiment. This way, they used complementary methods that point towards the same interpretation: the connection between preSMA and STN is crucial for inhibition, and IFG manipulates that connection.

So if you really truly want to not do something, your best way forward is to increase the activity in your preSMA and particularly in your IFG, which will then tell your STN to put on the brakes and inhibit whatever M1 is trying to do.

 

References

Aron, A. R., Fletcher, P. C., Bullmore, E. T., Sahakian, B. J., & Robbins, T. W. (2003). Stop-signal inhibition disrupted by damage to right inferior frontal gyrus in humans. Nature neuroscience, 6(2), 115-116.

Eagle, D. M., Baunez, C., Hutcheson, D. M., Lehmann, O., Shah, A. P., & Robbins, T. W. (2008). Stop-signal reaction-time task performance: role of prefrontal cortex and subthalamic nucleus. Cerebral cortex, 18(1), 178-188.

Nachev, P., Wydell, H., O’neill, K., Husain, M., & Kennard, C. (2007). The role of the pre-supplementary motor area in the control of action. Neuroimage, 36, T155-T163.

Rae, C. L., Hughes, L. E., Anderson, M. C., & Rowe, J. B. (2015). The prefrontal cortex achieves inhibitory control by facilitating subcortical motor pathway connectivity. Journal of Neuroscience, 35(2), 786-794

The fear of being found out

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