Revisiting a classical theory of sensory specificity: assessing consistency and stability of thermosensitive spots.

Thermal sensitivity is not uniform across the skin, and is particularly high in small (∼1 mm2) regions termed "thermosensitive spots." These spots are thought to reflect the anatomical location of specialized thermosensitive nerve endings from single primary afferents. Thermosensitive spots provide foundational support for "labeled line" or specificity theory of sensory perception, which states that different sensory qualities are transmitted by separate and specific neural pathways. This theory predicts a highly stable relation between repetitions of a thermal stimulus and the resulting sensory quality, yet these predictions have rarely been tested systematically. Here, we present the qualitative, spatial, and repeatability properties of 334 thermosensitive spots on the dorsal forearm sampled across four separate sessions. In line with previous literature, we found that spots associated with cold sensations (112 cold spots, 34%) were more frequent than spots associated with warm sensations (41 warm spots, 12%). Still more frequent (165 spots, 49%) were spots that elicited inconsistent sensations when repeatedly stimulated by the same temperature. Remarkably, only 13 spots (4%) conserved their position between sessions. Overall, we show unexpected inconsistency of both the perceptual responses elicited by spot stimulation and of spot locations across time. These observations suggest reappraisals of the traditional view that thermosensitive spots reflect the location of individual thermosensitive, unimodal primary afferents serving as specific labeled lines for corresponding sensory qualities.NEW & NOTEWORTHY Thermosensitive spots are clustered rather than randomly distributed and have the highest density near the wrist. Surprisingly, we found that thermosensitive spots elicit inconsistent sensory qualities and are unstable over time. Our results question the widely believed notion that thermosensitive spots reflect the location of individual thermoreceptive, unimodal primary afferents that serve as labelled lines for corresponding sensory qualities.

Learning from informative losses boosts the sense of agency.

Sense of agency, the feeling of having control over one's actions, is modulated by whether one's choices lead to desired or undesired outcomes. Learning similarly depends on outcome values from previous experience. In the current study, we evaluate a possible link between the sense of agency and learning, by investigating how intentional binding, an implicit measure of agency, changes during a probabilistic learning task. In two experiments, we show increased intentional binding in trials that follow losses, compared with trials that follow wins. Experiment 1 demonstrated that this post-error agency boost (PEAB) effect is rule-specific, as it did not occur if the trial following an error involved different action-outcome contingencies. Furthermore, PEAB was not modulated by the type of outcome presentation (monetary vs. affective). Experiment 2 showed that the PEAB effect can also occur when the current action involves a forced (as opposed to free) choice, but only when the previous, loss-provoking action was chosen freely. Thus, PEAB occurs when current actions are informed by outcomes of one's own previous action choices. Electroencephalography (EEG) data linked these effects to two event-related potential components, namely, the Feedback Related Negativity and the P300. Taken together, these results support the notion that PEAB reflects an adaptive property of human sense of agency, facilitating effective learning about the action-outcome structure of a specific task, to optimise future performance. By clarifying the conditions for enhancing the sense of agency through learning, this work adds to our understanding of human learning and agency.

Dopamine boosts intention and action awareness in Parkinson's disease.

Dopaminergic deficiency in Parkinson's disease (PD) has been associated with underactivation of the supplementary motor area and a reduction of voluntary actions. In these patients, awareness of intention to act has been shown to be delayed. However, delayed awareness of intention to act has also been shown in patients with hyperdopaminergic states and an excess of unwilled movements, as in Tourette's, and in patients with functional movement disorders. Hence, the role of dopamine in the awareness of intention and action remains unclear. 36 PD patients were tested ON and OFF dopaminergic medication and compared with 35 healthy age-matched controls. In addition, 17 PD patients with subthalamic deep brain stimulation (DBS) were tested ON medication and ON and OFF stimulation. Participants judged either the moment a self-generated action was performed, or the moment the urge to perform the action was felt, using the "Libet method". Temporal judgments of intention and action awareness were comparable between unmedicated PD patients and controls. Dopaminergic medication boosted anticipatory awareness of both intentions and actions in PD patients, relative to an unmedicated condition. The difference between ON/OFF DBS was not statistically reliable. Functional improvement of motor ability in PD through dopaminergic supplementation leads to earlier awareness of both intention, and of voluntary action.

Learning volition: A longitudinal study of developing intentional awareness in Tourette syndrome.

Tourette syndrome (TS) is characterized by the presence of involuntary movements (tics) which are, at least partly, generated within 'voluntary' motor pathways. Here we reassess 16 TS patients (age 19 ± 2.3 years) who participated in a mental chronometry study of volition 5.5 years previously (Ganos C et al. Cortex. 2015 Mar.; 64:47-54), and 16 age-matched controls. Participants estimated the time of their own voluntary movements (Libet's M judgement), or of conscious intention to make voluntary movements (Libet's W judgement), in separate blocks. We considered M judgement as a control condition. Therefore, the experience of an intention to move occurring prior to actual movement onset, as measured by the W-M gap, was taken as the cardinal feature of volition. Time estimates of the TS group did not differ significantly from controls, for either M or W judgement. Further, M and W time estimates in the TS group had not changed significantly between the two assessments. However, exploratory analyses revealed a strong relation between disease duration and the development of M- and W-judgements: the longer was the disease duration, the less was the developmental increase in the W-M gap (linear regression, p = .003). In conclusion, our results suggest compromised development of experience of volition in developing TS patients. The developmental difficulty in processing internal premotor signals for voluntary actions could reflect the chronic persistence of tics from adolescence to adulthood.

Enhanced perceptual processing of self-generated motion: Evidence from steady-state visual evoked potentials.

The sense of agency emerges when our voluntary actions produce anticipated or predictable outcomes in the external world. It remains unclear how the sense of control also influences our perception of the external world. The present study examined perceptual processing of self-generated motion versus non-self-generated motion using steady-state visual evoked potentials (SSVEPs). Participants continuously moved their finger on a touchpad to trigger the movements of two shapes (Experiment 1) or two groups of dots (Experiment 2) on a monitor. Degree of control was manipulated by varying the spatial relation between finger movement and stimulus trajectory across conditions. However, the velocity, onset time, and offset time of visual stimuli always corresponded to participants' finger movement. Stimuli flickered at a frequency of either 7.5 Hz or 10 Hz, thus SSVEPs of these frequencies and their harmonics provided a frequency-tagged measurement of perceptual processing. Participants triggered the motion of all stimuli simultaneously, but had greater levels of control over some stimuli than over others. Their task was to detect a brief colour change on the border(s) of one shape (Experiment 1) or of one group of dots (Experiment 2). Although control over shapes/dots was irrelevant to the visual detection task, we found stronger SSVEPs for stimuli that were under a high level of control, compared with the stimuli that were under a low level of control. Our results suggest that the spatial regularity between self-generated movements and visual input boosted the neural responses underlying perceptual processing. Our results support the preactivation account of sensory attenuation, suggesting that perceptual processing of self-generated events is enhanced rather than inhibited.

Try and try again: Post-error boost of an implicit measure of agency.

The sense of agency refers to the feeling that we control our actions and, through them, effects in the outside world. Reinforcement learning provides an important theoretical framework for understanding why people choose to make particular actions. Few previous studies have considered how reinforcement and learning might influence the subjective experience of agency over actions and outcomes. In two experiments, participants chose between two action alternatives, which differed in reward probability. Occasional reversals of action-reward mapping required participants to monitor outcomes and adjust action selection processing accordingly. We measured shifts in the perceived times of actions and subsequent outcomes ('intentional binding') as an implicit proxy for sense of agency. In the first experiment, negative outcomes showed stronger binding towards the preceding action, compared to positive outcomes. Furthermore, negative outcomes were followed by increased binding of actions towards their outcome on the following trial. Experiment 2 replicated this post-error boost in action binding and showed that it only occurred when people could learn from their errors to improve action choices. We modelled the post-error boost using an established quantitative model of reinforcement learning. The post-error boost in action binding correlated positively with participants' tendency to learn more from negative outcomes than from positive outcomes. Our results suggest a novel relation between sense of agency and reinforcement learning, in which sense of agency is increased when negative outcomes trigger adaptive changes in subsequent action selection processing.

Having control over the external world increases the implicit sense of agency.

The sense of agency refers to the feeling of control over one's actions, and, through them, over external events. One proposed marker of implicit sense of agency is 'intentional binding'-the tendency to perceive voluntary actions and their outcomes as close in time. Another is attenuation of the sensory consequences of a voluntary action. Here we show that the ability to choose an outcome through action selection contributes to implicit sense of agency. We measured intentional binding and stimulus intensity ratings using painful and non-painful somatosensory outcomes. In one condition, participants chose between two actions with different probabilities of producing high or low intensity outcomes, so action choices were meaningful. In another condition, action selection was meaningless with respect to the outcome. Having control over the outcome increased binding, especially when outcomes were painful. Greater sensory attenuation also tended to be associated with stronger binding of the outcome towards the action that produced it. Previous studies have emphasised the link between sense of agency and initiation of voluntary motor actions. Our study shows that the ability to control outcomes by discriminative action selection is another key element of implicit sense of agency. It also investigates, for the first time, the relation between binding and sensory attenuation for the same events.

Motor-evoked potentials reveal a motor-cortical readout of evidence accumulation for sensorimotor decisions.

Many everyday activities require time-pressured sensorimotor decision making. Traditionally, perception, decision, and action processes were considered to occur in series, but this idea has been successfully challenged, particularly by neurophysiological work in animals. However, the generality of parallel processing requires further elucidation. Here, we investigate whether the accumulation of a decision can be observed intrahemispherically within human motor cortex. Participants categorized faces as male or female, with task difficulty manipulated using morphed stimuli. Transcranial magnetic stimulation, applied during the reaction-time interval, produced motor-evoked potentials (MEPs) in two hand muscles that were the major contributors when generating the required pinch/grip movements. Smoothing MEPs using a Gaussian kernel allowed us to recover a continuous time-varying MEP average, comparable to an EEG component, permitting precise localization of the time at which the motor plan for the responding muscle became dominant. We demonstrate decision-related activity in the motor cortex during this perceptual discrimination task, suggesting ongoing evidence accumulation within the motor system even for two independent actions represented within one hemisphere.

A Roving Dual-Presentation Simultaneity-Judgment Task to Estimate the Point of Subjective Simultaneity.

The most popular tasks with which to investigate the perception of subjective synchrony are the temporal order judgment (TOJ) and the simultaneity judgment (SJ). Here, we discuss a complementary approach-a dual-presentation (2x) SJ task-and focus on appropriate analysis methods for a theoretically desirable "roving" design. Two stimulus pairs are presented on each trial and the observer must select the most synchronous. To demonstrate this approach, in Experiment 1 we tested the 2xSJ task alongside TOJ, SJ, and simple reaction-time (RT) tasks using audiovisual stimuli. We interpret responses from each task using detection-theoretic models, which assume variable arrival times for sensory signals at critical brain structures for timing perception. All tasks provide similar estimates of the point of subjective simultaneity (PSS) on average, and PSS estimates from some tasks were correlated on an individual basis. The 2xSJ task produced lower and more stable estimates of model-based (and thus comparable) sensory/decision noise than the TOJ. In Experiment 2 we obtained similar results using RT, TOJ, ternary, and 2xSJ tasks for all combinations of auditory, visual, and tactile stimuli. In Experiment 3 we investigated attentional prior entry, using both TOJs and 2xSJs. We found that estimates of prior-entry magnitude correlated across these tasks. Overall, our study establishes the practicality of the roving dual-presentation SJ task, but also illustrates the additional complexity of the procedure. We consider ways in which this task might complement more traditional procedures, particularly when it is important to estimate both PSS and sensory/decisional noise.

Endogenous Action Selection Processes in Dorsolateral Prefrontal Cortex Contribute to Sense of Agency: A Meta-Analysis of tDCS Studies of 'Intentional Binding'.

BACKGROUND: Sense of agency is the experience of being in control of one's own actions and their consequences. The role of frontal cortex in this aspect of action control and awareness remains unclear. OBJECTIVE/HYPOTHESIS: Given the role of dorsolateral prefrontal cortex (DLPFC) in action selection, we predicted that DLPFC may contribute to sense of agency when participants select between multiple actions. METHODS: We performed a series of experiments by manipulating a range of task parameters related to action selection and action outcomes while participants were exposed to tDCS stimulation of the left DLPFC. We measured the temporal association between a voluntary action and its outcome using the intentional binding effect, as an implicit measure of sense of agency. RESULTS: Fixed-effect meta-analysis of our primary data showed a trend towards a frontal tDCS, together with considerable heterogeneity between our experiments. Classifying the experiments into subsets of studies, according to whether participants endogenously selected between alternative actions or not, explained 71% of this heterogeneity. Anodal stimulation of DLPFC increased the temporal binding of actions towards tones in the subset of studies involving endogenous action selection, but not in the other studies. CONCLUSIONS: DLPFC may contribute to sense of agency when participants selected between multiple actions. This enhanced feeling of control over voluntary actions could be related to the observed therapeutic effects of frontal tDCS in depression.