The role of motor inhibition during covert speech production

Covert speech is accompanied by a subjective multisensory experience with auditory and kinaesthetic components. An influential hypothesis states that these sensory percepts result from a simulation of the corresponding motor action that relies on the same internal models recruited for the control of overt speech. This simulationnist view raises the question of how it is possible to imagine speech without executing it. In this perspective, we discuss the possible role(s) played by motor inhibition during covert speech production. We suggest that considering covert speech as an inhibited form of overt speech maps naturally to the purported progressive internalisation of overt speech during childhood. However, we argue that the role of motor inhibition may differ widely across different forms of covert speech (e.g., condensed vs. expanded covert speech) and that considering this variety helps reconciling seemingly contradictory findings from the neuroimaging literature.

Snapping out of Autopilot: Overriding Habits in Real Time and the Role of Ventrolateral Prefrontal Cortex

Habits allow environmental and interoceptive cues to trigger behavior in an automatized fashion, making them liable to deployment in inappropriate or outdated contexts. Over the long-term, repeated failure of a once adaptive habit to satisfy current goals produces extinction learning that suppresses the habit’s execution. Less attention has been afforded to the mechanisms underlying real-time habit suppression: the capacity to stop the execution of a cued habit that is goal-conflicting. Here, we first posit a model by which goal-relevant stimuli can 1) bring unfolding habits and their projected outcomes into awareness, 2) prompt evaluation of the habit outcome with respect to current goals, and 3) trigger cessation of the habit response if it is determined to be goal-conflicting. Second, we propose a modified stop-signal task to test this model of “goal-directed stopping of habit execution”. Finally, we marshal evidence indicating that the ventrolateral prefrontal cortex (vlPFC), situated at the nexus of salience detection, action-plan assessment, and motor inhibition networks, is uniquely positioned to coordinate the overriding of habitual behaviors in real time. In sum, this review presents a testable model and candidate neurobiological substrate for our capacity to “snap out of autopilot” and override goal-conflicting habits in real time.

How Does Task Presentation Impact Motor Inhibition Performance in Young Children?

Peg tapping tasks are commonly used as a measure of inhibitory skill in young children. However, differences in the way the task is presented may influence children’s performance. For example, if a peg tapping task is presented at regular intervals, children can entrain to the presentation pulse, which may in turn support their performance. This study assessed how speed and regularity of presentation may support or impair children’s responses. An experimenter was filmed delivering the tapping task at two different speeds (120 bpm/3,000 ms per trial and 150 bpm/2,400 ms per trial). Additionally, they were filmed delivering the task at regular intervals (i.e., the onset of each trial was predictable), or at irregular intervals (the onset of each trial was unpredictable). N = 103 children aged between 5 and 6 years old were tested on the task. They completed one block with 20 regular interval trials and another block with 20 irregular interval trials. Block presentation order was randomized. Children who achieved over 90% accuracy on the task were then presented with two more blocks at 150 bpm. Children’s response accuracy was measured. Our results show a difference in children’s accuracy across all conditions with trials presented in an irregular manner producing poorer performance on the task. The study demonstrates how speed and regularity of presentation can affect children’s scores on a tapping task used to measure inhibition. Demands on working memory, motor ability, and speed of processing are all affected by adjustments in presentation. Entrainment to a pulse is also a potential mechanism employed by children to support their performance on this task.