Motor cortex-evoked activity in reciprocal muscles is modulated by reward probability

Effects of Paired Associative Stimulation on Cortical Plasticity in Agonist–Antagonist Muscle Representations

Paired associative stimulation (PAS) increases and decreases cortical excitability in primary motor cortex (M1) neurons, depending on the spike timing-dependent plasticity, i.e., long-term potentiation (LTP)- and long-term depression (LTD)-like plasticity, respectively. However, how PAS affects the cortical circuits for the agonist and antagonist muscles of M1 is unclear. Here, we investigated the changes in the LTP- and LTD-like plasticity for agonist and antagonist muscles during PAS: 200 pairs of 0.25-Hz peripheral electric stimulation of the right median nerve at the wrist, followed by a transcranial magnetic stimulation of the left M1 with an interstimulus interval of 25 ms (PAS-25 ms) and 10 ms (PAS-10 ms). The unconditioned motor evoked potential amplitudes of the agonist muscles were larger after PAS-25 ms than after PAS-10 ms, while those of the antagonist muscles were smaller after PAS-25 ms than after PAS-10 ms. The γ-aminobutyric acid A (GABAA)- and GABAB-mediated cortical inhibition for the agonist and antagonist muscles were higher after PAS-25 ms than after PAS-10 ms. The cortical excitability for the agonist and antagonist muscles reciprocally and topographically increased and decreased after PAS, respectively; however, GABAA and GABAB-mediated cortical inhibitory functions for the agonist and antagonist muscles were less topographically decreased after PAS-10 ms. Thus, PAS-25 ms and PAS-10 ms differentially affect the LTP- and LTD-like plasticity in agonist and antagonist muscles.

A possible anti-anxiety effect of appetitive aggression and a possible link to the work of Donald Winnicott

Various pleasant sensations that give a particularly intense pleasure are able to improve anxiety. In the present study I consider the possibility that their anti-anxiety action depends on the strong pleasure they provide, and I propose a possible mechanism of this action. According to some studies, also appetitive aggression (an aggression that provokes a strong pleasure and that is performed only for the pleasure it provides) can improve anxiety, and in this article I consider the possibility that the pleasure of appetitive aggression is able to reduce anxiety by the same mechanism I have proposed for other intense pleasurable sensations.

The aggression performed by a child against the mother or against a substitute for the mother in the first period of life (a period in which this aggression is not dangerous) is a recurring theme throughout the work of of Donald Winnicott. Winnicott stresses that this aggression is necessary for the normal development of the child, and that the child must be free to practise it. According to Winnicott, this aggression is highly pleasurable and is not a response to unpleasant or hostile external situations. For these characteristics it seems to correspond to appetitive aggression in the adult that has been found to be able to reduce anxiety. Consequently, aggression performed by the child in the first period of life may also relieve anxiety, in the same way that appetitive aggression helps against anxiety in the adult.

In his writings, Winnicott returns several times to an unthinkable or archaic anxiety that children experience when they feel abandoned by their mother for a period that is too long for them, and all children, according to Winnicott, live on the brink of this anxiety. In this study I propose the hypothesis that aggression in the early period of life may be necessary for children because the intense pleasure it provides may help them against this continuously impending anxiety.

Reward does not modulate corticospinal excitability in anticipation of a Stroop trial

Action preparation is associated with a transient decrease of corticospinal excitability just before target onset. We have previously shown that the prospect of reward modulates preparatory corticospinal excitability in a Simon task. While the conflict in the Simon task strongly implicates the motor system, it is unknown whether reward prospect modulates preparatory corticospinal excitability in tasks that implicate the motor system less directly. To that effect, we examined reward-modulated preparatory corticospinal excitability in the Stroop task. We administered a rewarded cue-target delay paradigm using Stroop stimuli that afforded a left or right index finger response. Single-pulse transcranial magnetic stimulation was administered over the left primary motor cortex and electromyography was obtained from the right first dorsal interosseous muscle. In line with previous findings, there was a preparatory decrease in corticospinal excitability during the delay period. In contrast to our previous study using the Simon task, preparatory corticospinal excitability was not modulated by reward. Our results indicate that reward-modulated changes in the motor system depend on specific task-demands, possibly related to varying degrees of motor conflict.

Differential Effect of Visual and Proprioceptive Stimulation on Corticospinal Output for Reciprocal Muscles

This study investigated the corticospinal excitability of reciprocal muscles during tasks involving sensory difference between proprioceptive and visual inputs. Participants were instructed to relax their muscles and to observe a screen during vibratory stimulation. A video screen was placed on the board covering the right hand and forearm. Participants were randomly tested in four conditions: resting, control, static, and dynamic. The resting condition involved showing a black screen, the control condition, a mosaic patterned static videoclip; the static condition, a static videoclip of wrist flexion 0°; and the dynamic condition, a videoclip that corresponded to each participant's closely-matched illusory wrist flexion angle and speed by vibration. Vibratory stimulation (frequency 80 Hz and duration 4 s) was applied to the distal tendon of the dominant right extensor carpi radialis (ECR) using a tendon vibrator in the control, static, and dynamic conditions. Four seconds after the vibratory stimulation (end of vibration), the primary motor cortex at the midpoint between the centers of gravity of the flexor carpi radialis (FCR) and ECR muscles was stimulated by transcranial magnetic stimulation (TMS). The ECR motor evoked potential (MEP) amplitudes significantly increased in the control condition compared to the resting condition, whereas the FCR MEP amplitudes did not change between the resting and control conditions. In addition, the ECR MEP amplitudes significantly increased in the static condition compared to the dynamic condition. However, the FCR MEP amplitudes significantly increased in the dynamic condition compared to the static condition. These results imply that the difference between visuo-proprioceptive information had an effect on corticospinal excitability for the muscle. In conclusion, we found that proprioceptive and visual information differentially altered the corticospinal excitability of reciprocal muscles.

Neurostimulation Therapies

Depression is one of the most disabling conditions in the world. In many cases patients continue to suffer with depressive disorders despite a series of adequate trials of medication and psychotherapy. Neuromodulation treatments offer a qualitatively different modality of treatment that can frequently prove efficacious in these treatment-refractory patients. The field of neuromodulation focuses on the use of electrical/electromagnetic energy, both invasively and noninvasively, to interface with and ultimately alter activity within the human brain for therapeutic purposes. These treatments provide another set of options to offer patients when clinically indicated, and knowledge of their safety, risks and benefits, and appropriate clinical application is essential for modern psychiatrists and other mental health professionals. Although neuromodulation techniques hold tremendous promise, only three such treatments are currently approved by the United States Food and Drug Administration (FDA) for the treatment of major depressive disorder: electroconvulsive therapy (ECT), vagus nerve stimulation (VNS), and repetitive transcranial magnetic stimulation (rTMS). Additionally, numerous other neurostimulation modalities (deep brain stimulation [DBS], magnetic seizure therapy [MST], transcranial electric stimulation [tES], and trigeminal nerve stimulation [TNS]), though currently experimental, show considerable therapeutic promise. Researchers are actively looking for ways to optimize outcomes and clinical benefits by making neuromodulation treatments safer, more efficacious, and more durable.

Reward anticipation changes corticospinal excitability during task preparation depending on response requirements and time pressure

The preparation of an action is accompanied by transient corticospinal (CS) excitability changes. Motivation can modulate these changes. Specifically, when a cue indicates that a reward can be obtained, CS excitability initially increases, followed by a pronounced decrease. This dynamic could reflect processes related to reward expectancy, processes related to action preparation, or a combination of both. Here we set up two experiments to dissociate these accounts. A rewarded choice reaction time task was used in which individuals were cued at the beginning of each trial whether or not a response would be required at target onset and whether or not a reward could be obtained. We used single-pulse transcranial magnetic stimulation (spTMS) over the left primary motor cortex (M1) early (shortly after cue onset) or late (shortly before target onset) preceding target onset to examine CS excitability during motivated action preparation. Electromyography (EMG) was obtained from the right first dorsal interosseous (FDI) muscle. In the first experiment, we used a lenient response deadline, whereas a strict response time-out procedure was employed in the second experiment. Reward modulated CS excitability differentially only in the second experiment: CS excitability was highest during reward anticipation for the early stimulation epoch and was reduced for the late stimulation epoch when individuals were required to prepare a response, while CS excitability remained unchanged during non-reward anticipation. Our findings suggest that the reward effect on CS excitability is dependent on the actual implementation of effort to attain reward (i.e., the preparation of an actual action), as well as on temporal requirements (i.e., time pressure) invoked by the task.

Changes in Magnitude and Variability of Corticospinal Excitability During Rewarded Time-Sensitive Behavior

Reward expectation and time estimation are important for behavior and affect corticospinal excitability. This study investigated changes in corticospinal excitability during rewarded time-sensitive behavioral tasks. The rewarded time-sensitive task comprised three fixed-ratio (FR) schedules: FR_A contained a reward stimulus after every response, FR_B after every two responses, and FR_C after every four responses. The participants were instructed to press a left button with the index finger as quickly as possible in response to the appearance of a red circle. Just after the left button press, the word “10-yen” (approximately $0.1) or “no pay” was presented as feedback. Then, the participant had to mentally estimate/wait for 2.5 s from pressing the left button to pressing the right button. One second after the reward stimulus, transcranial magnetic stimulation (TMS) was delivered to the primary motor cortex at the hotspot of the first dorsal interosseous (FDI) muscle. Each participant received items corresponding to the total monetary reward accumulated at the end of the experiment. The variability of motor evoked potential (MEP) amplitudes transformed from a random process during the resting state into an autoregressive process during the rewarded time-sensitive behavioral task. Additionally, the random variation of MEP amplitudes in the FR_C, FR_B, and FR_A schedules increased in a stepwise fashion. However, the magnitude of MEP amplitudes significantly increased for the FR_B and FR_C schedules compared to the FR_A schedule. The time estimation lag was negative for the three FR schedules but there was no difference among the three FR schedules. The magnitude of corticospinal excitability increased in low reward probability, whereas the variability of corticospinal excitability transformed into an autoregressive process in high reward probability. These results imply that the magnitude and variability of expectation-related corticospinal excitabilities can be differentially altered by reward probability.

The role of stimulus-driven versus goal-directed processes in fight and flight tendencies measured with motor evoked potentials induced by Transcranial Magnetic Stimulation

This study examines two contrasting explanations for early tendencies to fight and flee. According to a stimulus-driven explanation, goal-incompatible stimuli that are easy/difficult to control lead to the tendency to fight/flee. According to a goal-directed explanation, on the other hand, the tendency to fight/flee occurs when the expected utility of fighting/fleeing is the highest. Participants did a computer task in which they were confronted with goal-incompatible stimuli that were (a) easy to control and fighting had the highest expected utility, (b) easy to control and fleeing had the highest expected utility, and (c) difficult to control and fleeing and fighting had zero expected utility. After participants were trained to use one hand to fight and another hand to flee, they either had to choose a response or merely observe the stimuli. During the observation trials, single-pulse Transcranial Magnetic Stimulation (TMS) was applied to the primary motor cortex 450 ms post-stimulus onset and motor-evoked potentials (MEPs) were measured from the hand muscles. Results showed that participants chose to fight/flee when the expected utility of fighting/fleeing was the highest, and that they responded late when the expected utility of both responses was low. They also showed larger MEPs for the right/left hand when the expected utility of fighting/fleeing was the highest. This result can be interpreted as support for the goal-directed account, but only if it is assumed that we were unable to override the presumed natural mapping between hand (right/left) and response (fight/flight).

High-intensity transcranial magnetic stimulation reveals differential cortical contributions to prepared responses

Corticospinal output pathways have typically been considered to be the primary driver for voluntary movements of the hand/forearm; however, more recently, reticulospinal drive has also been implicated in the production of these movements. Although both pathways may play a role, the reticulospinal tract is thought to have stronger connections to flexor muscles than to extensors. Similarly, movements involuntarily triggered via a startling acoustic stimulus (SAS) are believed to receive greater reticular input than voluntary movements. To investigate a differential role of reticulospinal drive depending on movement type or acoustic stimulus, corticospinal drive was transiently interrupted using high-intensity transcranial magnetic stimulation (TMS) applied during the reaction time (RT) interval. This TMS-induced suppression of cortical drive leads to RT delays that can be used to assess cortical contributions to movement. Participants completed targeted flexion and extension movements of the wrist in a simple RT paradigm in response to a control auditory go signal or SAS. Occasionally, suprathreshold TMS was applied over the motor cortical representation for the prime mover. Results revealed that TMS significantly increased RT in all conditions. There was a significantly longer TMS-induced RT delay seen in extension movements than in flexion movements and a greater RT delay in movements initiated in response to control stimuli compared with SAS. These results suggest that the contribution of reticulospinal drive is larger for wrist flexion than for extension. Similarly, movements triggered involuntarily by an SAS appear to involve greater reticulospinal drive, and relatively less corticospinal drive, than those that are voluntarily initiated. NEW & NOTEWORTHY Through the use of the transcranial magnetic stimulation-induced silent period, we provide novel evidence for a greater contribution of reticulospinal drive, and a relative decrease in corticospinal drive, to movements involuntarily triggered by a startle compared with voluntary movements. These results also provide support for the notion that both cortical and reticular structures are involved in the neural pathway underlying startle-triggered movements. Furthermore, our results indicate greater reticulospinal contribution to wrist flexion than extension movements.

Goal Achievement Failure Drives Corticospinal Modulation in Promotion and Prevention Contexts

When making decisions, people are typically differently sensitive to gains and losses according to the motivational context in which the choice is performed. As hypothesized by Regulatory Focus Theory (RFT), indeed, goals are supposed to change in relation to the set of possible outcomes. In particular, in a promotion context, the goal is achieving the maximal gain, whereas in a prevention context it turns into avoiding the greatest loss. We explored the neurophysiological counterpart of this phenomenon, by applying Transcranial Magnetic Stimulation (TMS) and recording the motor evoked potentials (MEPs) in participants taking part in an economic game, in which they observed actions conveying different goal attainment levels, framed in different motivational contexts. More than the actual value of the economic exchange involved in the game, what affected motor cortex excitability was the goal attainment failure, corresponding to not achieving the maximal payoff in a promotion context and not avoiding the greatest snatch in a prevention context. Therefore, the results provide support for the key predictions of RFT, identifying a neural signature for the goal attainment failure.

A Possible Link between Anxiety and Schizophrenia and a Possible Role of Anhedonia

In the prodromal phase of schizophrenia, severe alterations of the visual appearance of the environment have been found, accompanied by a state of intense anxiety. The present study considers the possibility that these alterations really exist in the appearance of objects, but that healthy people do not see them. The image of the world that we see is continuously deformed and fragmented by foreshortenings, partial overlapping, and so on and must be constantly reassembled and interpreted; otherwise, it could change so much that we would hardly recognize it. Since pleasure has been found to be involved in visual and cognitive information processing, the possibility is considered that anhedonia (the reduction of the ability to feel pleasure) might interfere with the correct reconstruction and interpretation of the image of the environment and alter its appearance. The possibility is also considered that these alterations might make the environment hostile, might at times evoke the sensation of being trapped by a predator, and might be the cause of the anxiety that accompanies them. According to some authors, they might also induce delusional ideas, in an attempt to restore meaning in a world that has become chaotic and frightening.

Nonequivalent modulation of corticospinal excitability by positive and negative outcomes

OBJECTIVE

The difference between positive and negative outcomes is important in trial-and-error decision-making processes and affects corticospinal excitability. This study investigated corticospinal excitability during the performance of trial-and-error decision-making tasks with varying competing behavioral outcomes.

METHODS

Each trial began with one of five colored circles presented as a cue. Each color represented a different reward probability, ranging from 10% to 90%. The subjects were instructed to decide whether to perform wrist flexion in response to the cue. Two seconds after the presentation of the cue, a reward stimulus (picture of a coin) or penalty stimulus (mauve circle) was randomly presented to the subject. If the picture of a coin appeared, the subjects received the coin after the experiment if they had performed wrist flexion, but not if they had not performed wrist flexion. If a mauve circle appeared, a coin was deducted from the total reward if the subjects had performed wrist flexion, but not if they had not performed wrist flexion. One second after the reward or penalty stimulus, transcranial magnetic stimulation was delivered to the primary motor cortex at the midpoint between the centers of gravity of the flexor carpi radialis (agonist) and extensor carpi radialis (antagonist) muscles.

RESULTS

Cumulative wrist flexions were positively correlated with reward probabilities. Motor evoked potential (MEP) amplitudes in agonist muscles were significantly higher when wrist flexion incurred a penalty than when it incurred a reward, but there was no difference in the MEP amplitudes of antagonist muscles.

CONCLUSION

Positive and negative behavioral outcomes differentially altered behavior and corticospinal excitability, and unexpected penalties had a stronger effect on corticospinal excitability for agonist muscles.

Withholding a Reward-driven Action: Studies of the Rise and Fall of Motor Activation and the Effect of Cognitive Depletion

Controlling an inappropriate response tendency in the face of a reward-predicting stimulus likely depends on the strength of the reward-driven activation, the strength of a putative top-down control process, and their relative timing. We developed a rewarded go/no-go paradigm to investigate such dynamics. Participants made rapid responses (on go trials) to high versus low reward-predicting stimuli and sometimes had to withhold responding (on no-go trials) in the face of the same stimuli. Behaviorally, for high versus low reward stimuli, responses were faster on go trials, and there were more errors of commission on no-go trials. We used single-pulse TMS to map out the corticospinal excitability dynamics, especially on no-go trials where control is needed. For successful no-go trials, there was an early rise in motor activation that was then sharply reduced beneath baseline. This activation-reduction pattern was more pronounced for high- versus low-reward trials and in individuals with greater motivational drive for reward. A follow-on experiment showed that, when participants were fatigued by an effortful task, they made more errors on no-go trials for high versus low reward stimuli. Together, these studies show that, when a response is inappropriate, reward-predicting stimuli induce early motor activation, followed by a top-down effortful control process (which we interpret as response suppression) that depends on the strength of the preceding activation. Our findings provide novel information about the activation-suppression dynamics during control over reward-driven actions, and they illustrate how fatigue or depletion leads to control failures in the face of reward.

Modulation of corticospinal excitability by reward depends on task framing

Findings from previous transcranial magnetic stimulation (TMS) experiments suggest that the primary motor cortex (M1) is sensitive to reward conditions in the environment. However, the nature of this influence on M1 activity is poorly understood. The dopamine neuron response to conditioned stimuli encodes reward probability and outcome uncertainty, or the extent to which the outcome of a situation is known. Reward uncertainty and probability are related: uncertainty is maximal when probability is 0.5 and minimal when probability is 0 or 1 (i.e., certain outcome). Previous TMS-reward studies did not examine these factors independently. Here, we used single-pulse TMS to measure corticospinal excitability in 40 individuals while they performed a simple computer task, making guesses to find or avoid a hidden target. The task stimuli implied three levels of reward probability and two levels of uncertainty. We found that reward probability level interacted with the trial search condition. That is, motor evoked potential (MEP) amplitude, a measure of corticospinal neuron excitability, increased with increasing reward probability when participants were instructed to "find" a target, but not when they were instructed to "avoid" a target. There was no effect of uncertainty on MEPs. Response times varied with the number of choices. A subset of participants also received paired-pulse stimulation to evaluate changes in short-intracortical inhibition (SICI). No effects of SICI were observed. Taken together, the results suggest that the reward-contingent modulation of M1 activity reflects reward probability or a related aspect of utility, not outcome uncertainty, and that this effect is sensitive to the conceptual framing of the task.