Learning about trial sequences disrupts the partial reinforcement extinction effect in classical conditioning.

The partial reinforcement extinction effect (PREE) refers to the phenomenon that conditioned responding extinguishes more slowly if subjects had been inconsistently ("partially") reinforced than if they had been reinforced on every trial ("continuously" reinforced). One largely successful account of the PREE, known as sequential theory (Capaldi, 1966), suggests that, when subjects are partially reinforced, they learn that memories of sequences of nonreinforced trials are associated with subsequent reinforcement. This association helps to maintain responding (i.e., delay extinction) when the subjects experience nonreinforced trials during extinction. Sequential theory's explanation of the PREE hinges on subjects learning sequences of nonreinforced trials during acquisition. However, direct evidence for such sequential learning is not available in previous studies of the PREE where animals are trained with multiple sequences of different lengths that are randomly intermixed and, therefore, cannot anticipate whether a given trial will be reinforced during acquisition. The current study conducted two experiments that trained rats with a single fixed trial sequence to provide evidence of sequential learning during conditioning, and then observe its effect on the PREE. Under one condition the rats did learn about the fixed sequence but did not subsequently show a PREE, whereas other rats that did show a PREE had not learned the trial sequences during conditioning. Therefore, contrary to sequential theory's prediction, our result suggests that learning about the trial sequence is neither necessary nor sufficient for the PREE. We suggest that the PREE may instead depend on uncertainty about whether the conditioned stimulus will be reinforced. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

The effect of staircase stopping accuracy and testing environment on stop-signal reaction time.

The stop-signal task is widely used in experimental psychology and cognitive neuroscience research, as well as neuropsychological and clinical practice for assessing response inhibition. The task requires participants to make speeded responses on a majority of trials, but to inhibit responses when a stop signal appears after the imperative cue. The stop-signal delay after the onset of the imperative cue determines how difficult it is to cancel an initiated action. The delay is typically staircased to maintain a 50% stopping accuracy for an estimation of stopping speed to be calculated. However, the validity of this estimation is compromised when participants engage in strategic slowing, motivated by a desire to avoid stopping failures. We hypothesized that maintaining stopping accuracy at 66.67% reduces this bias, and that slowing may also be impacted by the level of experimenter supervision. We found that compared with 50%, using a 66.67% stopping accuracy staircase produced slower stop-signal reaction time estimations (≈7 ms), but resulted in fewer strategic slowing exclusions. Additionally, both staircase procedures had similar within-experiment test-retest reliability. We also found that while individual and group testing in a laboratory setting produced similar estimations of stopping speed, participants tested online produced slower estimates. Our findings indicate that maintaining stopping accuracy at 66.67% is a reliable method for estimating stopping speed and can have benefits over the standard 50% staircase procedure. Further, our results show that care should be taken when comparing between experiments using different staircases or conducted in different testing environments.

The sequencing of trials during partial reinforcement affects subsequent extinction.

If a conditioned stimulus or response has been inconsistently ("partially") reinforced, conditioned responding will take longer to extinguish than if responding had been established by consistent ("continuous") reinforcement. This partial reinforcement extinction effect (PREE) is one of the best-known phenomena in associative learning but defies ready explanation by associative models which assume that a partial reinforcement schedule will produce weaker conditioning that should be less resistant to extinction. The most popular explanation of the PREE is that, during partial reinforcement, animals learn that recent nonreinforced (N) trials are associated with subsequent reinforcement (R), and therefore the presence of N trials during extinction serves to promote generalization of conditioning to extinction. According to sequential theory (Capaldi, 1966), animals can encode whole sequences (runs) of N trials and associate their memory of the sequence with subsequent R. The length of these N sequences during conditioning affects how long the animal will continue to respond during extinction. The present experiment used Pavlovian magazine approach conditioning with rats to test two predictions of this theory. Consistent with sequential theory, the PREE was sensitive to the length of the N sequence: conditioning with long sequences (runs of 3-5 N trials) produced a stronger PREE than conditioning with short sequences (runs of 1 or 2) even when the total number of N and R trials was held constant. Surprisingly, there was no PREE among rats trained with the short sequences. Moreover, contrary to the theory's prediction, interrupting the long N sequences with reinforced trials of a different conditioned stimulus did not affect the subsequent PREE. I conclude that uncertainty about reinforcement, rather than the memory of N sequences per se, is a key factor in the development of the PREE. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Is cortical inhibition in primary motor cortex related to executive control?

Recent research using paired-pulse transcranial magnetic stimulation (TMS) has shown that the speed with which people can stop an action is linked to GABAergic inhibitory activity in the motor system. Specifically, a significant proportion of the variance in stop signal reaction time (SSRT; a widely used measure of inhibitory control) is accounted for by short-interval cortical inhibition (SICI). It is still unclear whether this relationship reflects a broader link between GABAergic processes and executive functions, or a specific link between GABAergic processes and motor stopping ability. The current study sought to replicate the correlation between SSRT and SICI while investigating whether this association generalises to other measures of inhibitory control and working memory, and to long-interval cortical inhibition (LICI). Participants completed a battery of inhibition (Stop-Signal, Stroop, Flanker) and working memory (n-back, Digit Span, and Operation Span) tasks. We replicated the correlation between SICI and SSRT but found no other correlations between behavioural measures of executive control and the two cortical measures of inhibition. These findings indicate that the relationship between SSRT and SICI is specific to a particular property of response inhibition and likely reflects the function of local inhibitory networks mediated by GABAA.

The learning curve, revisited.

The nature of the operations that support learning should be evident in the form or shape of the learning curve. For example, models that describe learning as an iterative error-correction process expect that the amount learned on each trial follows a decelerating (negatively inflected) function. That prediction is broadly consistent with the shape of the acquisition and extinction curves derived from mean measures of response strength. However, such evidence can be flawed because group means may not accurately portray the response curves of individual subjects in a conditioning experiment. Moreover, such evidence relies on strong assumptions about the way that what has been learned is expressed in responding. The current work presents a new analytical approach to reveal the rate of change in responding across the course of conditioning in individual animals. When applied to the conditioning and extinction data from a large sample of rats, this analysis confirms that responses are acquired and extinguish gradually and, in both cases, follow a decelerating learning curve. That is, changes in responding are largest at the start of conditioning or extinction and get progressively smaller as responding approaches an asymptote. However, rather than conforming to the specific shape predicted by an error-correction process, the results suggest that the amount learned increases according to a logarithmic function such that responding during conditioning and extinction is proportional to the log of the number of trials. The implications of these findings for models of associative learning are discussed. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Delaying extinction weakens the partial reinforcement extinction effect.

Conditioned responding that has been extinguished can spontaneously return when the conditioned stimulus (CS) is first presented after an extended delay. This spontaneous recovery of responding suggests that the memory of nonreinforced experience with the CS is impaired over the delay period. Rescorla (2007) provided evidence that this effect of time on nonreinforcement is not specific to extinction. He showed that a delay period can also reverse the reduction of responding established by a partial reinforcement schedule. Here we describe a series of experiments that attempted to confirm Rescorla's finding and additionally assessed the impact of the delay on another well-known consequence of partial reinforcement-the partial reinforcement extinction effect (PREE). Like Rescorla, we used a Pavlovian conditioning procedure with rats, measuring magazine activity during a CS that signaled food. Unlike Rescorla, we did not find that responding acquired under partial reinforcement spontaneously increased after a delay; however, we did observe a significant reduction in the PREE after that delay. We conclude that the passage of time has a selective effect on the retrieval of memories of nonreinforcement. Therefore, time produces spontaneous recovery by impairing retrieval of extinction memories but also weakens the PREE by impairing retrieval of memories of nonreinforcement that were acquired during partial reinforcement. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Does the time-span of conditioning affect spontaneous recovery after extinction?

Gold-standard psychological treatments such as exposure therapy are significantly undermined by high relapse rates. Although exposure-based treatments are capable of extinguishing maladaptive behaviours, these behaviours often spontaneously re-emerge over time - a phenomenon known in experimental research as spontaneous recovery. Understanding the factors that underlie this process is essential to improving long-term treatment outcomes. One factor that is yet to be properly examined is the effect of the total span of time across which behaviours are learned. To date, only one study by Gallistel & Papachristos (2020) has explored this in mice. Their findings suggest that long spans of acquisition learning result in greater spontaneous recovery compared to short spans. We investigated the effect of conditioning span across 5 experiments using rats. Contrary to Gallistel & Papachristos, our results found no difference in recovery between rats conditioned over a long span versus a short span, following short, intermediate and long delay intervals. This suggests that the span of conditioning does not affect the magnitude of recovery, nor the rate at which recovery emerges. Unexpectedly, conditioning span did appear to influence the strength of responding during acquisition, such that longer conditioning spans led to higher levels of responding. This finding could indicate that the learning process operates over a long time period beyond the original training episode. However, further research is needed to establish whether conditioning span influences the strength of what is learned, or instead the performance of a conditioned response.

In anticipation of pain: expectancy modulates corticospinal excitability, autonomic response, and pain perception.

ABSTRACT: Pain is a ubiquitous experience encompassing perceptual, autonomic, and motor responses. Expectancy is known to amplify the perceived and autonomic components of pain, but its effects on motor responses are poorly understood. Understanding expectancy modulation of corticospinal excitability has important implications regarding deployment of adaptive and maladaptive protective behaviours in anticipation of pain. We developed a protocol to compare corticospinal excitability to expected high pain, expected low pain, and critically low pain when high pain was expected. Expecting high pain suppressed corticospinal excitability and heightened perceptual and autonomic responses to the low-pain stimulus, as with increased noxious stimulation (ie, expected high pain). Multilevel modelling revealed that perceived pain mediated the effect of both noxious stimulation and this expectancy-modulated pain on autonomic responses, but corticospinal excitability did not. These results demonstrate that merely expecting pain influenced all pain components. Findings shed new light on the aetiology of expectancy-modulated pain, whereby expecting pain mobilises the motor system to protect the body from harm by a protective withdrawal reflex, associated with reduced corticospinal excitability, and activates similar processes as increased nociceptive stimulation. This has significant practical implications for the treatment of pain, particularly in scenarios where avoidance of pain-related movement contributes to its maintenance.

Working memory load reduces corticospinal suppression to former go and trained no-go cues.

Environmental cues associated with an action can prime the motor system, decreasing response times and activating motor regions of the brain. However, when task goals change, the same responses to former go-associated cues are no longer required and motor priming needs to be inhibited to avoid unwanted behavioural errors. The present study tested whether the inhibition of motor system activity to presentations of former go cues is reliant on top-down, goal-directed cognitive control processes using a working memory (WM) load manipulation. Applying transcranial magnetic stimulation over the primary motor cortex to measure motor system activity during a Go/No-go task, we found that under low WM, corticospinal excitability was suppressed to former go and trained no-go cues relative to control cues. Under high WM, the cortical suppression to former go cues was reduced, suggesting that the underlying mechanism required executive control. Unexpectedly, we found a similar result for trained no-go cues and showed in a second experiment that the corticospinal suppression and WM effects were unrelated to local inhibitory function as indexed by short-interval intracortical inhibition. Our findings reveal that the interaction between former response cues and WM is complex and we discuss possible explanations of our findings in relation to models of response inhibition.

Motor cortex dysfunction in problem gamblers.

Impairments in response inhibition have been implicated in gambling psychopathology. This behavioral impairment may suggest that the neural mechanisms involved in response inhibition, such as GABAA -mediated neurotransmission in the primary motor cortex (M1), are also impaired. The present study obtained paired-pulse transcranial magnetic stimulation markers of GABAA and glutamate receptor activity from the left M1 of three groups-problem gamblers (n = 17, 12 males), at-risk gamblers (n = 29, 19 males), and controls (n = 23, six males)-with each group matched for alcohol use, substance use, and attention-deficit hyperactivity disorder (ADHD) symptomology. Response inhibition was measured using the stop signal task. Results showed that problem gamblers had weaker M1 GABAA receptor activity relative to controls and elevated M1 glutamate receptor activity relative to at-risk gamblers and controls. Although there were no differences in response inhibition between the groups, poorer response inhibition was correlated with weaker M1 GABAA receptor activity. These findings are the first to show that problem gambling is associated with alterations in M1 GABAA and glutamate-mediated neurotransmission.

Expected TMS excites the motor system less effectively than unexpected stimulation.

The brain's response to sensory input is modulated by prediction. For example, sounds that are produced by one's own actions, or those that are strongly predicted by environmental cues, elicit an attenuated N1 component in the auditory evoked potential. It has been suggested that this form of sensory attenuation to stimulation produced by one's own actions is the reason we are unable to tickle ourselves. Here we examined whether the neural response to direct stimulation of the brain is attenuated by prediction in a similar manner. Transcranial magnetic stimulation (TMS) applied over primary motor cortex can be used to gauge the excitability of the motor system. Motor-evoked potentials (MEPs), elicited by TMS and measured in peripheral muscles, are larger when actions are being prepared and smaller when actions are voluntarily suppressed. We tested whether the amplitude of MEPs was attenuated under circumstances where the TMS pulse can be reliably predicted, even though control of the relevant motor effector was never required. Self-initiation of the TMS pulse and reliable cuing of the TMS pulse both produced attenuated MEP amplitudes, compared to those generated programmatically in an unpredictable manner. These results suggest that predictive coding may be governed by domain-general mechanisms responsible for all forms predictive learning. The findings also have important methodological implications for designing TMS experiments that control for the predictability of TMS pulses.

Linking cortical and behavioural inhibition: Testing the parameter specificity of a transcranial magnetic stimulation protocol.

Across a series of studies, our laboratory has shown that the efficiency of action stopping is associated with the strength of GABAA-mediated short-intracortical inhibition (SICI) as measured using transcranial magnetic stimulation (TMS). However, these studies used fixed TMS parameters, which may not optimally probe GABAA receptor activity for each individual. In the present study, we measured the relationship between stopping efficiency and SICI using a range of TMS parameters. Participants completed a right-hand unimanual stop signal task to obtain a measure of stopping efficiency. Resting-state SICI was measured from the left primary motor cortex using six combinations of interstimulus intervals and conditioning pulse intensities. We also established the parameters which generated the strongest SICI (SICImax) and weakest SICI (SICImin) for each individual. We found that stopping efficiency was significantly predicted by SICI using various TMS parameters, including SICImax. Interestingly, SICImin accounted for a similar proportion of variance in stopping efficiency as SICI measured using other TMS parameters. The findings suggest that the relationship between stopping efficiency and SICI is robust, reliable, and not influenced by the extent to which SICI is optimally probed.

Stop Signal Task Training Strengthens GABA-mediated Neurotransmission within the Primary Motor Cortex.

We have recently shown that the efficiency in stopping a response, measured using the stop signal task, is related to GABAA-mediated short-interval intracortical inhibition (SICI) in the primary motor cortex. In this study, we conducted two experiments on humans to determine whether training participants in the stop signal task within one session (Experiment 1) and across multiple sessions (Experiment 2) would increase SICI strength. For each experiment, we obtained premeasures and postmeasures of stopping efficiency and resting-state SICI, that is, during relaxed muscle activity (Experiment 1, n = 45, 15 male participants) and SICI during the stop signal task (Experiment 2, n = 44, 21 male participants). In the middle blocks of Experiment 1 and the middle sessions of Experiment 2, participants in the experimental group completed stop signal task training, whereas control participants completed a similar task without the requirement to stop a response. After training, the experimental group showed increased resting-state SICI strength (Experiment 1) and increased SICI strength during the stop signal task (Experiment 2). Although there were no overall behavioral improvements in stopping efficiency, improvements at an individual level were correlated with increases in SICI strength at rest (Experiment 1) and during successful stopping (Experiment 2). These results provide evidence of neuroplasticity in resting-state and task-related GABAA-mediated SICI in the primary motor cortex after response inhibition training. These results also suggest that SICI and stopping efficiency are temporally linked, such that a change in SICI between time points is correlated with a change in stopping efficiency between time points.

Pavlovian conditioning under partial reinforcement: The effects of nonreinforced trials versus cumulative conditioned stimulus duration.

A core feature of associative models, such as those proposed by Allan Wagner (Rescorla & Wagner, 1972; Wagner, 1981), is that conditioning proceeds in a trial-by-trial fashion, with increments and decrements in associative strength occurring on each occasion that the conditioned stimulus (conditional stimulus, or CS) is present either with or without the unconditioned stimulus (US). A very different approach has been taken by theories that assume animals continuously accumulate information about the total length of time spent waiting for the US both during the CS and in the absence of the CS (e.g., Gallistel & Gibbon, 2000). Here we describe 3 experiments using within-subject designs that tested trial-based and time-accumulation accounts of the acquisition of conditioned responding using magazine approach conditioning in rats. We found that responding was affected by the total (cumulative) duration of exposure to the CS without the US rather than the number of trials on which the CS occurred without the US. We also found that exposure to the CS without the US had the same effect on conditioning whether that exposure occurred shortly (60 s) before each CS-US pairing or whether it occurred long (240 s) before each pairing. These findings are more consistent with time-accumulation models of conditioning than trial-based models like the Rescorla-Wagner model and Wagner's (1981) sometimes opponent process model. We discuss these findings in relation to other evidence that favors trial-based models rather than time-accumulation models. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Binding identity and orientation in object recognition.

We tested whether an object's orientation is inherently bound to its identity in a holistic view-based representation at the early stages of visual identification, or whether identity and orientation are represented separately. Observers saw brief and masked stimulus sequences containing two rotated objects. They had to detect if a previously cued object was present in the sequence and report its orientation. In Experiments 1 and 2, the objects were presented sequentially in the same spatial location for 70 ms each, whereas in Experiments 3 and 4 they were presented simultaneously in different spatial locations for 70 ms and 140 ms, respectively. Across all experiments, observers reported the correct orientation for approximately 70% of the positively identified objects, and were at chance in reporting the orientation when they had not recognized the object. This finding suggests that orientation information is accessed after an object has been identified. In addition, when the two objects were presented sequentially in the same spatial location, orientation errors were not random-observers tended to report the orientation of the alternative object in the sequence, indicating misbindings between the identities and orientations of objects that share spatial location. This susceptibility to binding errors was not observed when the objects were in different spatial locations. These results suggest that identity and orientation may be prone to misbinding, and that spatial location may serve to protect their joint integrity.

The importance of trials.

Many theories of conditioning describe learning as a process by which stored information about the relationship between a conditioned stimulus (CS) and unconditioned stimulus (US) is progressively updated upon each occasion (trial) that the CS occurs with, or without, the US. These simple trial-based descriptions can provide a powerful and efficient means of extracting information about the correlation between 2 events, but they fail to explain how animals learn about the timing of events. This failure has motivated models of conditioning in which animals learn continuously, either by explicitly representing temporal intervals between events or by sequentially updating an array of associations between temporally distributed elements of the CS and US. Here, I review evidence that some aspects of conditioning are not the consequence of a continuous learning process but reflect a trial-based process. In particular, the way that animals learn about the absence of a predicted US during extinction suggests that they encode and remember trials as single complete episodes rather than as a continuous experience of unfulfilled expectation of the US. These memories allow the animal to recognize repeated instances of nonreinforcement and encode these as a sequence that, in the case of a partial reinforcement schedule, can become associated with the US. The animal is thus able to remember details about the pattern of a CS's reinforcement history, information that affects how long the animal continues to respond to the CS when all reinforcement ceases. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The partial reinforcement extinction effect depends on learning about nonreinforced trials rather than reinforcement rate.

Conditioned responding extinguishes more slowly after partial (inconsistent) reinforcement than after consistent reinforcement. This Partial Reinforcement Extinction Effect (PREE) is usually attributed to learning about nonreinforcement during the partial schedule. An alternative explanation attributes it to any difference in the rate of reinforcement, arguing that animals can detect the change to nonreinforcement more quickly after a denser schedule than a leaner schedule. Experiments 1a and 1b compared extinction of magazine responding to a conditioned stimulus (CS) reinforced with 1 food pellet per trial and a CS reinforced with 2 pellets per trial. Despite the difference in reinforcement rate, there was no reliable difference in extinction. Both experiments did demonstrate the conventional PREE comparing a partial CS (50% reinforced) with a consistent CS. Experiments 2 and 3 tested whether the PREE depends specifically on learning about nonreinforced trials during partial reinforcement. Rats were trained with 2 CS configurations, A and AX. One was partially reinforced, the other consistently reinforced. When AX was partial and A consistent, responding to AX extinguished more slowly than to A. When AX was consistent and A was partial, there was no difference in their extinction. Therefore, pairing X with partial reinforcement allowed rats to show a PREE to AX that did not generalize to A. Pairing A with partial reinforcement meant that rats showed a PREE to A that generalized to AX. Thus, the PREE depends on learning about nonreinforced trials during partial reinforcement and is not because of any difference in per-trial probability of reinforcement. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Contralateral and Ipsilateral Relationships between Intracortical Inhibition and Stopping Efficiency.

We have recently shown that the efficiency of stopping a response is correlated with GABAergic activity in primary motor cortex (M1) measured using the short interval intracortical inhibition (SICI) protocol. However, this finding was observed when SICI was measured in left M1 and when stopping efficiency was measured with a bimanual response task. The aim of the present study was to examine the extent to which the relationship between SICI and stopping is lateralized to the hemisphere controlling the response (e.g. left M1 and stopping a right hand response) and/or reflects bilateral inhibitory mechanisms (as might be seen between left M1 and left hand stopping). We measured resting SICI (i.e. during relaxed muscle activity) in left and right M1 and stopping efficiency in the left and right hand, in 38 healthy individuals. We found that SICI was significantly correlated between hemispheres (r = 0.51) and stopping efficiency was correlated between hands (r = 0.77). When controlling for other relevant variables, we found that stopping efficiency in each hand was uniquely predicted by SICI in the contralateral hemisphere, but not the ipsilateral hemisphere. These results suggest that there is a hemispheric-specific contribution of SICI to stopping efficiency.

Associatively-Mediated Suppression of Corticospinal Excitability: A Transcranial Magnetic Stimulation (TMS) Study.

Response inhibition - the suppression of prepotent behaviours when they are inappropriate - has been thought to rely on executive control. Against this received wisdom, it has been argued that external cues repeatedly associated with response inhibition can come to trigger response inhibition automatically without top-down command. The current project endeavoured to provide evidence for associatively-mediated motor inhibition. We tested the hypothesis that stop-associated stimuli can, in a bottom-up fashion, directly activate inhibitory mechanisms in the motor cortex. Human subjects were first trained on a stop-signal task. Once trained, the subjects received transcranial magnetic stimulation applied over their primary motor cortex during passive observation of either the stop signal (i.e. without any need to stop a response) or an equally familiar control stimulus never associated with stopping. Analysis of motor-evoked potentials showed that corticospinal excitability was reduced during exposure to the stop signal, which likely involved stimulus-driven activation of intracortical GABAergic interneurons. This result provides evidence that, through associative learning, stop-associated stimuli can engage local inhibitory processes at the level of the motor cortex.

Hierarchical and Nonlinear Dynamics in Prefrontal Cortex Regulate the Precision of Perceptual Beliefs.

Actions are shaped not only by the content of our percepts but also by our confidence in them. To study the cortical representation of perceptual precision in decision making, we acquired functional imaging data whilst participants performed two vibrotactile forced-choice discrimination tasks: a fast-slow judgment, and a same-different judgment. The first task requires a comparison of the perceived vibrotactile frequencies to decide which one is faster. However, the second task requires that the estimated difference between those frequencies is weighed against the precision of each percept-if both stimuli are very precisely perceived, then any slight difference is more likely to be identified than if the percepts are uncertain. We additionally presented either pure sinusoidal or temporally degraded "noisy" stimuli, whose frequency/period differed slightly from cycle to cycle. In this way, we were able to manipulate the perceptual precision. We report a constellation of cortical regions in the rostral prefrontal cortex (PFC), dorsolateral PFC (DLPFC) and superior frontal gyrus (SFG) associated with the perception of stimulus difference, the presence of stimulus noise and the interaction between these factors. Dynamic causal modeling (DCM) of these data suggested a nonlinear, hierarchical model, whereby activity in the rostral PFC (evoked by the presence of stimulus noise) mutually interacts with activity in the DLPFC (evoked by stimulus differences). This model of effective connectivity outperformed competing models with serial and parallel interactions, hence providing a unique insight into the hierarchical architecture underlying the representation and appraisal of perceptual belief and precision in the PFC.