Motivational goal-priming with or without awareness produces faster and stronger force exertion

Shouting strengthens voluntary force during sustained maximal effort through enhancement of motor system state via motor commands

Previous research indicates that shouting during momentary maximal exertion effort potentiates the maximal voluntary force through the potentiation of motor cortical excitability. However, the muscular force-enhancing effects of shouting on sustained maximal force production remain unclear. We investigated the effect of shouting on the motor system state by examining motor evoked potentials in response to transcranial magnetic stimulation applied over the hand area of the contralateral primary motor cortex (M1) during sustained maximal voluntary contraction, and by assessing handgrip maximal voluntary force. We observed that shouting significantly increased handgrip maximal voluntary force and reduced the silent period. Our results indicate that shouting increased handgrip voluntary force during sustained maximal exertion effort through the reduced silent period. This is the first objective evidence that the muscular force of shouting during maximal force exertion is associated with the potentiation of motor system activity produced by the additional drive of shouting operating on the motor system (i.e., shouting-induced excitatory input to M1).

Local and distributed cortical markers of effort expenditure during sustained goal pursuit

The adaptive adjustment of behavior in pursuit of desired goals is critical for survival. To accomplish this complex feat, individuals must weigh the potential benefits of a given action against time, energy, and resource costs. Here, we examine brain responses associated with willingness to exert physical effort during the sustained pursuit of desired goals. Our analyses reveal a distributed pattern of brain activity in aspects of ventral medial prefrontal cortex that tracks with trial-level variability in effort expenditure. Indicating the brain represents echoes of effort at the point of feedback, whole-brain searchlights identified signals reflecting past effort expenditure in medial and lateral prefrontal cortices, encompassing broad swaths of frontoparietal and dorsal attention networks. These data have important implications for our understanding of how the brain's valuation mechanisms contend with the complexity of real-world dynamic environments with relevance for the study of behavior across health and disease.

Shouting strengthens maximal voluntary force and is associated with augmented pupillary dilation

Previous research has demonstrated that human maximal voluntary force is generally limited by neural inhibition. Producing a shout during maximal exertion effort enhances the force levels of maximal voluntary contraction. However, the mechanisms underlying this enhancement effect on force production remain unclear. We investigated the influence of producing a shout on the pupil-linked neuromodulatory system state by examining pupil size. We also examined its effects on the motor system state by examining motor evoked potentials in response to transcranial magnetic stimulation applied over the contralateral primary motor cortex, and by evaluating handgrip maximal voluntary force. Analysis revealed that producing a shout significantly increased handgrip maximal voluntary force, followed by an increase in pupil size and a reduction of the cortical silent period. Our results indicate that producing a shout increased handgrip maximal voluntary force through the enhancement of motor cortical excitability, possibly via the enhancement of noradrenergic system activity. This study provides evidence that the muscular force-enhancing effect of shouting during maximal force exertion is related to both the motor system state and the pupil-linked neuromodulatory system state.

The unconscious mental inhibiting process of human maximal voluntary contraction

Human maximal voluntary contraction (MVC) is believed to be limited by neural inhibition. Motivational goal priming alters background states of the motor system, leading to enhanced MVC. However, the mechanisms that determine the constant inhibition of force exertion in the motor system remain unclear. The primary behavioural goal of MVC is maximal voluntary force exertion. The final expected or desired state of this behavioural goal is explicitly demonstrated with words related to physical exertion, such as 'maximal', irrespective of the possibility of demand-like properties in participants' minds, such as attainability and/or desirability of the goal. For the primed maximal goal state, most trial results fail to meet expectations, demonstrating negative affect that, without awareness, contributes to the mentioned inhibitory mechanism underlying MVC. We therefore speculated that the behavioural goal of MVC contributes to neural inhibitory mechanisms underlying MVC. In our study, we used a previously developed paradigm (Takarada and Nozaki in Scientific Reports 8: 10135, 2018) in which subliminal visual priming stimuli such as the physical exertion-related words "perform" and "exert" were presented to 12 healthy participants and were followed by supraliminal words that were the word "maximal" or neutral.We found that when combined with the term 'maximal' in the consciously visible form, the effect of this subliminal motor-goal priming in inducing pupil dilation and stronger action preparation/execution was abolished without conscious awareness. This is the first objective evidence of motor inhibitory effect-predicting patterns of pupil-linked noradrenergic activity as a signature of a type of mental inhibition underlying the MVC behavioural goal.

Habits and Goals in Human Behavior: Separate but Interacting Systems

People automatically repeat behaviors that were frequently rewarded in the past in a given context. Such repetition is commonly attributed to habit, or associations in memory between a context and a response. Once habits form, contexts directly activate the response in mind. An opposing view is that habitual behaviors depend on goals. However, we show that this view is challenged by the goal independence of habits across the fields of social and health psychology, behavioral neuroscience, animal learning, and computational modeling. It also is challenged by direct tests revealing that habits do not depend on implicit goals. Furthermore, we show that two features of habit memory-rapid activation of specific responses and resistance to change-explain the different conditions under which people act on habit versus persuing goals. Finally, we tested these features with a novel secondary analysis of action-slip data. We found that habitual responses are activated regardless of goals, but they can be performed in concert with goal pursuit.

Effects of Mental Effort on Premotor Muscle Activity and Maximal Grip Force

The present study sought to evaluate how mental effort modulates premotor activity within forearm muscles in the context of an isometric grasping task. Muscle activity of the flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC) was recorded during the application of maximum grip forces in nineteen healthy adult subjects. Each subject was examined under two experimental conditions: 1) spontaneous initiation of grasp (SI) and 2) focused concentration preceding the initiation of grasp (CA). Two novel parameters, the mean premotor duration (MPD) and the mean premotor power (MPP) were used to distinguish patterns of muscle activity. Here we tested the hypothesis was maximal grip strength is primed by muscle activity during the premotor phase. Our results demonstrate that MPD for each muscle group was significantly longer in the CA condition than for the SI condition (BF₁₀ = 491497) and that MPP was significantly greater in EDC than in FDS (BF₁₀ = 4305). Furthermore, both the MPD and MPP of the EDC were significantly correlated with maximum grip force. These results suggest that the increase of premotor activity consequent to the mental effort (focused concentration) may support internal biomechanical and physiological mechanisms which serve to enhance patterns of neuromuscular synergies.