Philippe Boulinguez

Stimulation of the subthalamic nucleus and impulsivity: release your horses.

In Parkinson disease (PD) patients, deep brain stimulation (DBS) of the subthalamic nucleus (STN) may contribute to certain impulsive behavior during high‐conflict decisions. A neurocomputational model of the basal ganglia has recently been proposed that suggests this behavioral aspect may be related to the role played by the STN in relaying a “hold your horses” signal intended to allow more time to settle on the best option. The aim of the present study was 2‐fold: 1) to extend these observations by providing evidence that the STN may influence and prevent the execution of any response even during low‐conflict decisions; and 2) to identify the neural correlates of this effect.

Have we been asking the right questions when assessing response inhibition in go/no-go tasks with fMRI? A meta-analysis and critical review

The popular go/no-go paradigm is supposed to ensure a reliable probing of response inhibition mechanisms. Functional magnetic resonance imaging (fMRI) studies have repeatedly found a large number of structures, usually including a right lateralized parieto-frontal network and the pre-supplementary motor area (pre-SMA). However, it is unlikely that all these regions are directly related to the mechanism that actively suppresses the motor command. Since most go/no-go designs involve complex stimulus identification/detection processes, these activations may rather reflect the engagement of different cognitive processes that are intrinsically related and quite difficult to disentangle. The current critical review is based on repeated meta-analyses of 30 go/no-go fMRI experiments using the Activation Likelihood Estimate method to contrast studies using simple vs. complex stimuli. The results show that most of the activity typically elicited by no-go signals, including pre-SMA hemodynamic response, is actually driven by the engagement of high attentional or working memory resources, not by inhibitory processes per se. Implications for current methods and theories of inhibitory control are discussed, and new lines of inquiry are proposed.

Visual modulation of proprioceptive reflexes during movement

Previous research has demonstrated that feedback circuits such as reflexes can be tuned by setting their gains prior to movement onset during both posture and movement tasks. However, such a control strategy requires that perturbation contingencies be predicted during movement planning and that task goals remain fixed. Here we test the hypothesis that feedforward regulation of reflex circuits also occurs during the course of movement in response to changes in task goals. Participants reached to a visual target that was occasionally jumped on movement initiation, thus changing task goals. Reflex responses were elicited through a mechanical perturbation on the same trial, 100 ms after the target jump. Impedance to the perturbation was tuned to the direction of the preceding jump: reflex responses increased or decreased depending on whether the perturbation opposed or was consistent with the target jump. This modulation, although sensitive to the direction of the jump, was insensitive to jump amplitude, as tested in a follow-up experiment. Our findings thus suggest that modulation of reflex circuits occurs online, and is sensitive to changes in visual target information. In addition, our results suggest a two-level model for visuo-motor control that reflects hierarchical neural organization.

Proactive Inhibitory Control of Response as the Default State of Executive Control

Refraining from reacting does not only involve reactive inhibitory mechanisms. It was recently found that inhibitory control also relies strongly on proactive mechanisms. However, since most available studies have focused on reactive stopping, little is known about how proactive inhibition of response is implemented. Two behavioral experiments were conducted to identify the temporal dynamics of this executive function. They manipulated respectively the time during which inhibitory control must be sustained until a stimulus occurs, and the time limit allowed to set up inhibition before a stimulus occurs. The results show that inhibitory control is not set up after but before instruction, and is not transient and sporadic but sustained across time. Consistent with our previous neuroimaging findings, these results suggest that proactive inhibition of response is the default mode of executive control. This implies that top-down control of sensorimotor reactivity would consist of a temporary release (up to several seconds), when appropriate (when the environment becomes predictable), of the default locking state. This conclusion is discussed with regard to current anatomo-functional models of inhibitory control, and to methodological features of studies of attention and sensorimotor control.

Greater robustness of second order statistics than higher order statistics algorithms to distortions of the mixing matrix in blind source separation of human EEG: implications for single-subject and group analyses.

A mandatory assumption in blind source separation (BSS) of the human electroencephalogram (EEG) is that the mixing matrix remains invariant, i.e., that the sources, electrodes and geometry of the head do not change during the experiment. Actually, this is not often the case. For instance, it is common that some electrodes slightly move during EEG recording. This issue is even more critical for group independent component analysis (gICA), a method of growing interest, in which only one mixing matrix is estimated for several subjects. Indeed, because of interindividual anatomo-functional variability, this method violates the mandatory principle of invariance. Here, using simulated (experiments 1 and 2) and real (experiment 3) EEG data, we test how eleven current BSS algorithms undergo distortions of the mixing matrix. We show that this usual kind of perturbation creates non-Gaussian features that are virtually added to all sources, impairing the estimation of real higher order statistics (HOS) features of the actual sources by HOS algorithms (e.g., Ext-INFOMAX, FASTICA). HOS-based methods are likely to identify more components (with similar properties) than actual neurological sources, a problem frequently encountered by BSS users. In practice, the quality of the recovered signal and the efficiency of subsequent source localization are substantially impaired. Performing dimensionality reduction before applying HOS-based BSS does not seem to be a safe strategy to circumvent the problem. Second order statistics (SOS)-based BSS methods belonging to the less popular SOBI family class are much less sensitive to this bias.

The dorsal medial frontal cortex mediates automatic motor inhibition in uncertain contexts: Evidence from combined fMRI and EEG studies

Response inhibition is commonly thought to rely on voluntary, reactive, selective, and relatively slow prefrontal mechanisms. In contrast, we suggest here that response inhibition is achieved automatically, nonselectively, within very short delays in uncertain environments. We modified a classical go/nogo protocol to probe context‐dependent inhibitory mechanisms. Because no single neuroimaging method can definitely disentangle neural excitation and inhibition, we combined fMRI and EEG recordings in healthy humans. Any stimulus (go or nogo) presented in an uncertain context requiring action restraint was found to evoke activity changes in the supplementary motor complex (SMC) with respect to a control condition in which no response inhibition was required. These changes included: (1) An increase in event‐related BOLD activity, (2) an attenuation of the early (170 ms) event related potential generated by a single, consistent source isolated by advanced blind source separation, and (3) an increase in the evoked‐EEG Alpha power of this source. Considered together, these results suggest that the BOLD signal evoked by any stimulus in the SMC when the situation is unpredictable can be driven by automatic, nonselective, context‐dependent inhibitory activities. This finding reveals the paradoxical mechanisms by which voluntary control of action may be achieved. The ability to provide controlled responses in unpredictable environments would require setting‐up the automatic self‐inhibitory circuitry within the SMC. Conversely, enabling automatic behavior when the environment becomes predictable would require top‐down control to deactivate anticipatorily and temporarily the inhibitory set. Hum Brain Mapp 35:5517–5531, 2014.

Proactive inhibitory control varies with task context

The goal of executive control is to adjust our behaviour to the environment. It involves not only the continuous planning and adaptation of actions but also the inhibition of inappropriate movements. Recently, a proactive form of inhibitory control has been shown, demonstrating that actions can be withheld, in an uncertain environment, thanks to the proactive locking of the mechanism by which motor commands are triggered (e.g. while waiting at traffic lights in a dense pedestrian zone, one will refrain in anticipation of a brisk acceleration when the green light comes on). However, little is known about this executive function and it remains unclear whether the overall amount of inhibitory control can be modulated as a function of the context. Here, we show that the level of this control varies parametrically as a function of the exogenous and endogenous factors setting the task context. We also show that the level of implemented proactive inhibitory control is dynamically readjusted to match the implicit temporal structure of the environment. These observations are discussed in relation to possible underlying functional substrates and related neurological and psychiatric pathologies.

Attention to baseline: does orienting visuospatial attention really facilitate target detection?

Standard protocols testing the orientation of visuospatial attention usually present spatial cues before targets and compare valid-cue trials with invalid-cue trials. The valid/invalid contrast results in a relative behavioral or physiological difference that is generally interpreted as a benefit of attention orientation. However, growing evidence suggests that inhibitory control of response is closely involved in this kind of protocol that requires the subjects to withhold automatic responses to cues, probably biasing behavioral and physiological baselines. Here, we used two experiments to disentangle the inhibitory control of automatic responses from orienting of visuospatial attention in a saccadic reaction time task in humans, a variant of the classical cue-target detection task and a sustained visuospatial attentional task. Surprisingly, when referring to a simple target detection task in which there is no need to refrain from reacting to avoid inappropriate responses, we found no consistent evidence of facilitation of target detection at the attended location. Instead, we observed a cost at the unattended location. Departing from the classical view, our results suggest that reaction time measures of visuospatial attention probably relie on the attenuation of elementary processes involved in visual target detection and saccade initiation away from the attended location rather than on facilitation at the attended location. This highlights the need to use proper control conditions in experimental designs to disambiguate relative from absolute cueing benefits on target detection reaction times, both in psychophysical and neurophysiological studies.

Contribution of insula in Parkinson's disease: A quantitative meta-analysis study.

The insula region is known to be an integrating hub interacting with multiple brain networks involved in cognitive, affective, sensory, and autonomic processes. There is growing evidence suggesting that this region may have an important role in Parkinsons disease (PD). Thus, to investigate the functional organization of the insular cortex and its potential role in parkinsonian features, we used a coordinate‐based quantitative meta‐analysis approach, the activation likelihood estimation. A total of 132 insular foci were selected from 96 published experiments comprising the five functional categories: cognition, affective/behavioral symptoms, bodily awareness/autonomic function, sensorimotor function, and nonspecific resting functional changes associated with the disease. We found a significant convergence of activation maxima related to PD in different insular regions including anterior and posterior regions bilaterally. This study provides evidence of an important functional distribution of different domains within the insular cortex in PD, particularly in relation to nonmotor aspects, with an influence of medication effect. Hum Brain Mapp 37:1375‐1392, 2016.

EMG as a key tool to assess motor lateralization and hand reaction time asymmetries

Inconsistent and conflicting results about hand reaction time (RT) asymmetries have led to controversies over lateralization and hemispheric specialization for visuomotor transformations. In this paper, we propose a methodological solution to separate the central and peripheral processes that may be differently involved in simple visuomotor asymmetries. We provide empirical data from a simple RT task that suggests that fractionating RT into motor and premotor components with respect to a change in the electromyographic activity is necessary to disentangle motor and premotor lateralization patterns. These results call for a refinement of classical studies of visuomotor transformations using electrophysiological correlates of embedded but unrelated asymmetries rather than overt psychophysical measurements alone.