On Task by David Badre

Author:David Badre
Language: eng
Format: epub
Publisher: Princeton University Press
Published: 2020-09-09T00:00:00+00:00

How does this pathway induce stopping? Connections from the right ventrolateral prefrontal cortex (R VLPFC) and dorsomedial prefrontal cortex descend to a subcortical structure called the subthalamic nucleus. These pathways presumably transmit some contextual information about the conditions for stopping. Excitatory neurons in the subthalamic nucleus then project to the globus pallidus. You may recall from chapter 3 that the globus pallidus inhibits thalamocortical drive and prevents movement, so this pathway through the subthalamic nucleus can influence the globus pallidus in only a couple synapses and rapidly clamp down on cortical activity for a response. Doing so bypasses the striatum and the slower deliberations going on between Go and NoGo cells. This means even if the Go pathway has decided to gate out an action, such as a left-hand response to an arrow, this fast pathway through the subthalamic nucleus can rapidly slam on the brakes before this happens.

Though not without controversy, the evidence for this model of fast inhibitory control through the subthalamic nucleus is some of the strongest in the field, much of it owing to the rigorous and elegant work of scientists like Trevor Robbins at the University of Cambridge and cognitive neuroscientist Adam Aron at the University of California San Diego (UCSD) and their collaborators.

First, there is evidence that each of the structures in this network is necessary for stopping. In an early report, Aron and Robbins observed that the amount of damage to the right ventrolateral prefrontal cortex in stroke patients negatively correlated with their strength of stopping, as measured by stop-signal reaction time.18 Importantly, these stopping deficits did not follow from damage to regions of the frontoparietal control system we associate with selective gating. This dissociation again points to separate control functions served by the frontoparietal control system we’ve discussed to this point and this inhibitory network.19

Moreover, this inhibitory network is, indeed, a network in that these regions work together to enact fast stopping. The cortical members of the network and the subthalamic nucleus are connected by direct white-matter tracts, allowing for fast communication between them, and the integrity of these connections correlates with the strength of stopping.20 Further, studies of stopping in both humans and animals have found a signature increase in low-frequency neural oscillations among these regions that is closely tied to the onset of inhibition.21 In other words, just before people stop their responses, chatter increases in this network and on a signature bandwidth, much like tuning in a particular channel on a shortwave radio.

Interestingly, chatter in the brain also increases on this signature bandwidth when people are surprised.22 We have all been surprised by an unexpected event. A door suddenly slams, someone puts a hand on our shoulder from behind, a dog starts barking behind a fence we are passing, or a deer crosses the road in front of our car. Some of these events demand a fast change in our behavior, like the deer; others might not, like the door slamming. But what these events have in common is

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