A general mechanism for decision-making in the human brain?

Betting on Non-Invasive Brain Stimulation to Treat Gambling Disorder: A Systematic Review and Meta-Analysis

Gambling disorder (GD) is a behavioral addiction that severely impacts individuals' functioning, leading to high socioeconomic costs. Non-invasive brain stimulation (NiBS) has received attention for treating psychiatric and neurological conditions in recent decades, but there is no recommendation for its use for GD. Therefore, this study aimed to systematically review and analyze the available literature to determine the effectiveness of NiBS in treating GD. Following the PRISMA guidelines, we screened four electronic databases up to July 2022 and selected relevant English-written original articles. We included ten papers in the systematic review and seven in the meta-analysis. As only two studies employed a sham-controlled design, the pre-post standardized mean change (SMCC) was computed as effect size only for real stimulation. The results showed a significant effect of NiBS in reducing craving scores (SMCC = -0.69; 95% CI = [-1.2, -0.2], p = 0.010). Moreover, considering the GD's frequent comorbidity with mood disorders, we ran an exploratory analysis of the effects of NiBS on depressive symptoms, which showed significant decreases in post-treatment scores (SMCC = -0.71; 95% CI = [-1.1, -0.3], p < 0.001). These results provide initial evidence for developing NiBS as a feasible therapy for GD symptoms but further comprehensive research is needed to validate these findings. The limitations of the available literature are critically discussed.

Potential mechanisms underlying the accelerated cognitive decline in people with chronic low back pain: A scoping review

A growing body of evidence has shown that people with chronic low back pain (CLBP) demonstrate significantly greater declines in multiple cognitive domains than people who do not have CLBP. Given the high prevalence of CLBP in the ever-growing aging population that may be more vulnerable to cognitive decline, it is important to understand the mechanisms underlying the accelerated cognitive decline observed in this population, so that proper preventive or treatment approaches can be developed and implemented. The current scoping review summarizes what is known regarding the potential mechanisms underlying suboptimal cognitive performance and cognitive decline in people with CLBP and discusses future research directions. Five potential mechanisms were identified based on the findings from 34 included studies: (1) altered activity in the cortex and neural networks; (2) grey matter atrophy; (3) microglial activation and neuroinflammation; (4) comorbidities associated with CLBP; and (5) gut microbiota dysbiosis. Future studies should deepen the understanding of mechanisms underlying this association so that proper prevention and treatment strategies can be developed.

A Causal Role for the Right Dorsolateral Prefrontal Cortex in Avoidance of Risky Choices and Making Advantageous Selections

In everyday life, risky decision-making relies on multiple cognitive processes including sensitivity to reinforcers, exploration, learning, and forgetting. Neuroimaging evidence suggests that the dorsolateral prefrontal cortex (DLPFC) is involved in exploration and risky decision-making, but the nature of its computations and its causal role remain uncertain. We provide evidence for the role of the DLPFC in value-independent, directed exploration on the Iowa Gambling Task (IGT) and we describe a new computational model to account for the competition of directed exploration and exploitation in guiding decisions. Forty-two healthy human participants were included in a right DLPFC, left DLPFC or sham stimulation groups using continuous theta-burst stimulation (cTBS). Immediately after cTBS, the IGT was completed. Computational modelling was used to account for exploration and exploitation with different combinations with value-based and sensitivity to reinforcers for each group. Applying cTBS to the left and right DLPFC selectively decreased directed exploration on the IGT compared to sham stimulation. Model-based analyses further indicated that the right (but not the left) DLPFC stimulation increased sensitivity to reinforcers, leading to avoidance of risky choices and promoting advantageous choices during the task. Although these findings are based on small sample sizes per group, they nevertheless elucidate the causal role of the right DLPFC in governing the exploration-exploitation tradeoff during decision-making in uncertain and ambiguous contexts.

Sex and region-specific effects of high fat diet on PNNs in obesity susceptible rats

Perineuronal nets (PNNs) are specialized extracellular matrix structures that primarily surround fast-spiking parvalbumin (PV)-containing interneurons within the PFC. They regulate PV neuron function and plasticity to maintain cortical excitatory/inhibitory balance. For example, reductions in PNN intensity are associated with reduced local inhibition and enhanced pyramidal neuron firing. We previously found that exposure to dietary high fat reduced PNN intensity within the PFC of male Sprague-Dawley (SD) rats. However, how high fat affects PNNs in the PFC of females or in obesity-vulnerable vs. -resistant models is unknown. Therefore, we gave male and female SD, selectively bred obesity-prone (OP), and obesity-resistant rats (OR) free access to standard lab chow or 60% high fat for 21 days. We then measured the number of PNN positive cells and PNN intensity (determined by Wisteria floribunda agglutinin [WFA] staining) as well as the number of PV positive neurons using immunohistochemistry. We found sex and region-specific effects of dietary high fat on PNN intensity, in the absence of robust changes in cell number. Effects were comparable in SD and OP but differed in OR rats. Specifically, high fat reduced PNN intensities in male SD and OP rats but increased PNN intensities in female SD and OP rats. In contrast, effects in ORs were opposite, with males showing increases in PNN intensity and females showing a reduction in intensity. Finally, these effects were also region specific, with diet-induced reductions in PNN intensity found in the prelimbic PFC (PL-PFC) and ventral medial orbital frontal cortex (vmOFC) of SD and OP males in the absence of changes in the infralimbic PFC (IL-PFC), and increases in PNN intensity in the IL-PFC of SD and OP females in the absence of changes in other regions. These results are discussed in light of roles PNNs may play in influencing PFC neuronal activity and the differential role of these sub-regions in food-seeking and motivation.

Sensory and decisional components of endogenous attention are dissociable

Endogenous cueing of attention enhances sensory processing of the attended stimulus (perceptual sensitivity) and prioritizes information from the attended location for guiding behavioral decisions (spatial choice bias). Here, we test whether sensitivity and bias effects of endogenous spatial attention are under the control of common or distinct mechanisms. Human observers performed a multialternative visuospatial attention task with probabilistic spatial cues. Observers' behavioral choices were analyzed with a recently developed multidimensional signal detection model (the m-ADC model). The model effectively decoupled the effects of spatial cueing on sensitivity from those on spatial bias and revealed striking dissociations between them. Sensitivity was highest at the cued location and not significantly different among uncued locations, suggesting a spotlight-like allocation of sensory resources at the cued location. On the other hand, bias varied systematically with cue validity, suggesting a graded allocation of decisional priority across locations. Cueing-induced modulations of sensitivity and bias were uncorrelated within and across subjects. Bias, but not sensitivity, correlated with key metrics of prioritized decision-making, including reaction times and decision optimality indices. In addition, we developed a novel metric, differential risk curvature, for distinguishing bias effects of attention from those of signal expectation. Differential risk curvature correlated selectively with m-ADC model estimates of bias but not with estimates of sensitivity. Our results reveal dissociable effects of endogenous attention on perceptual sensitivity and choice bias in a multialternative choice task and motivate the search for the distinct neural correlates of each.NEW & NOTEWORTHY Attention is often studied as a unitary phenomenon. Yet, attention can both enhance the perception of important stimuli (sensitivity) and prioritize such stimuli for decision-making (bias). Employing a multialternative spatial attention task with probabilistic cueing, we show that attention affects sensitivity and bias through dissociable mechanisms. Specifically, the effects on sensitivity alone match the notion of an attentional "spotlight." Our behavioral model enables quantifying component processes of attention, and identifying their respective neural correlates.

Task-Relevant Information Modulates Primary Motor Cortex Activity Before Movement Onset

Monkey neurophysiology research supports the affordance competition hypothesis (ACH) proposing that cognitive information useful for action selection is integrated in sensorimotor areas. In this view, action selection would emerge from the simultaneous representation of competing action plans, in parallel biased by relevant task factors. This biased competition would take place up to primary motor cortex (M1). Although ACH is plausible in environments affording choices between actions, its relevance for human decision making is less clear. To address this issue, we designed an functional magnetic resonance imaging (fMRI) experiment modeled after monkey neurophysiology studies in which human participants processed cues conveying predictive information about upcoming button presses. Our results demonstrate that, as predicted by the ACH, predictive information (i.e., the relevant task factor) biases activity of primary motor regions. Specifically, first, activity before movement onset in contralateral M1 increases as the competition is biased in favor of a specific button press relative to activity in ipsilateral M1. Second, motor regions were more tightly coupled with fronto-parietal regions when competition between potential actions was high, again suggesting that motor regions are also part of the biased competition network. Our findings support the idea that action planning dynamics as proposed in the ACH are valid both in human and non-human primates.

Behavioral preference in sequential decision-making and its association with anxiety

In daily life, people often make consecutive decisions before the ultimate goal is reached (i.e., sequential decision-making). However, this kind of decision-making has been largely overlooked in the literature. The current study investigated whether behavioral preference would change during sequential decisions, and the neural processes underlying the potential changes. For this purpose, we revised the classic balloon analogue risk task and recorded the electroencephalograph (EEG) signals associated with each step of decision-making. Independent component analysis performed on EEG data revealed that four EEG components elicited by periodic feedback in the current step predicted participants' decisions (gamble vs. no gamble) in the next step. In order of time sequence, these components were: bilateral occipital alpha rhythm, bilateral frontal theta rhythm, middle frontal theta rhythm, and bilateral sensorimotor mu rhythm. According to the information flows between these EEG oscillations, we proposed a brain model that describes the temporal dynamics of sequential decision-making. Finally, we found that the tendency to gamble (as well as the power intensity of bilateral frontal theta rhythms) was sensitive to the individual level of trait anxiety in certain steps, which may help understand the role of emotion in decision-making.

Response repetition biases in human perceptual decisions are explained by activity decay in competitive attractor models

Animals and humans have a tendency to repeat recent choices, a phenomenon known as choice hysteresis. The mechanism for this choice bias remains unclear. Using an established, biophysically informed model of a competitive attractor network for decision making, we found that decaying tail activity from the previous trial caused choice hysteresis, especially during difficult trials, and accurately predicted human perceptual choices. In the model, choice variability could be directionally altered through amplification or dampening of post-trial activity decay through simulated depolarizing or hyperpolarizing network stimulation. An analogous intervention using transcranial direct current stimulation (tDCS) over left dorsolateral prefrontal cortex (dlPFC) yielded a close match between model predictions and experimental results: net soma depolarizing currents increased choice hysteresis, while hyperpolarizing currents suppressed it. Residual activity in competitive attractor networks within dlPFC may thus give rise to biases in perceptual choices, which can be directionally controlled through non-invasive brain stimulation.

Effects of anodal tDCS of the lower limb M1 on ankle reaction time in young adults

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that modulates cortical excitability and influences motor behavior. There is limited information available regarding the effects of anodal tDCS on lower limb reaction time. In this study, we aimed to investigate the effects of anodal tDCS on lower limb simple reaction time (SRT) and choice reaction time (CRT). We probed this question further by examining the effects of anodal tDCS of the lower limb M1 on an upper limb RT task and a cognitive measure. Fourteen healthy young adults received anodal tDCS and sham tDCS to the lower limb M1 on two separate testing days in a counterbalanced order. After stimulation, we assessed the effects of tDCS on ankle dorsiflexion SRT and CRT, ankle plantarflexion SRT and CRT, wrist extension SRT and CRT and the symbol digit modality test (SDMT). Anodal tDCS significantly improved response times from baseline for ankle CRT but not for ankle SRT or wrist SRT or CRT. A significant decrement (i.e., longer response time) was noted for the sham tDCS conditions. There was a significant difference between anodal and sham conditions for all RT tasks, suggesting that anodal tDCS improved RT compared to sham. No change in SDMT scores was observed for both conditions. Anodal tDCS appeared to differentially modulate ankle SRT and CRT, suggesting an influence of anodal tDCS on complex motor processes and/or the supplementary motor area. Absence of effects on wrist CRT or SDMT suggests a spatial specificity of the influence of tDCS. Anodal tDCS also appears to potentially negate the effects of fatigue or task switching that was detrimental to RT in the sham condition.

Anodal Stimulation of the Left DLPFC Increases IGT Scores and Decreases Delay Discounting Rate in Healthy Males

Previous correlational imaging studies have implicated the dorsolateral prefrontal cortex (DLPFC) in decision making. Using High-Definition Transcranial Direct Current Stimulation (HD-tDCS), the present study directly investigated the causal role of the DLPFC in performing the Iowa Gambling Task (IGT) and the Inter-Temporal Choice (ITC) task. Three experiments were conducted: Experiment 1 (N = 41) to study the left DLPFC, Experiment 2 (N = 49) to study the right DLPFC, and Experiment 3 (N = 20, a subset of those in Experiment 1) to switch the experimental and control conditions. All participants were healthy male college students. For Experiments 1 and 2, participants were randomly assigned to either the HD-tDCS or the sham stimulation condition. For Experiment 3, participants were assigned to the condition they were not in during Experiment 1. Results showed that HD-tDCS over the left DLPFC increased IGT score, decreased the recency parameter in IGT, and lowered delay discounting rate (k) in the ITC task. We discussed the potential roles of impulse control and time perception in mediating the effect of tDCS stimulation of left DLPFC on decision making. Our results have clinical implications for the treatment of disorders involving poor decision-making, such as addictions.

Evidence Accumulation and Choice Maintenance Are Dissociated in Human Perceptual Decision Making

Perceptual decision making in monkeys relies on decision neurons, which accumulate evidence and maintain choices until a response is given. In humans, several brain regions have been proposed to accumulate evidence, but it is unknown if these regions also maintain choices. To test if accumulator regions in humans also maintain decisions we compared delayed and self-paced responses during a face/house discrimination decision making task. Computational modeling and fMRI results revealed dissociated processes of evidence accumulation and decision maintenance, with potential accumulator activations found in the dorsomedial prefrontal cortex, right inferior frontal gyrus and bilateral insula. Potential maintenance activation spanned the frontal pole, temporal gyri, precuneus and the lateral occipital and frontal orbital cortices. Results of a quantitative reverse inference meta-analysis performed to differentiate the functions associated with the identified regions did not narrow down potential accumulation regions, but suggested that response-maintenance might rely on a verbalization of the response.

Action Planning and the Timescale of Evidence Accumulation

Perceptual decisions are based on the temporal integration of sensory evidence for different states of the outside world. The timescale of this integration process varies widely across behavioral contexts and individuals, and it is diagnostic for the underlying neural mechanisms. In many situations, the decision-maker knows the required mapping between perceptual evidence and motor response (henceforth termed “sensory-motor contingency”) before decision formation. Here, the integrated evidence can be directly translated into a motor plan and, indeed, neural signatures of the integration process are evident as build-up activity in premotor brain regions. In other situations, however, the sensory-motor contingencies are unknown at the time of decision formation. We used behavioral psychophysics and computational modeling to test if knowledge about sensory-motor contingencies affects the timescale of perceptual evidence integration. We asked human observers to perform the same motion discrimination task, with or without trial-to-trial variations of the mapping between perceptual choice and motor response. When the mapping varied, it was either instructed before or after the stimulus presentation. We quantified the timescale of evidence integration under these different sensory-motor mapping conditions by means of two approaches. First, we analyzed subjects’ discrimination threshold as a function of stimulus duration. Second, we fitted a dynamical decision-making model to subjects’ choice behavior. The results from both approaches indicated that observers (i) integrated motion information for several hundred ms, (ii) used a shorter than optimal integration timescale, and (iii) used the same integration timescale under all sensory-motor mappings. We conclude that the mechanisms limiting the timescale of perceptual decisions are largely independent from long-term learning (under fixed mapping) or rapid acquisition (under variable mapping) of sensory-motor contingencies. This conclusion has implications for neurophysiological and neuroimaging studies of perceptual decision-making.

Representation of accumulating evidence for a decision in two parietal areas

Decisions are often made by accumulating evidence for and against the alternatives. The momentary evidence represented by sensory neurons is accumulated by downstream structures to form a decision variable, linking the evolving decision to the formation of a motor plan. When decisions are communicated by eye movements, neurons in the lateral intraparietal area (LIP) represent the accumulation of evidence bearing on the potential targets for saccades. We now show that reach-related neurons from the medial intraparietal area (MIP) exhibit a gradual modulation of their firing rates consistent with the representation of an evolving decision variable. When decisions were communicated by saccades instead of reaches, decision-related activity was attenuated in MIP, whereas LIP neurons were active while monkeys communicated decisions by saccades or reaches. Thus, for decisions communicated by a hand movement, a parallel flow of sensory information is directed to parietal areas MIP and LIP during decision formation.

Neural substrates of approach-avoidance conflict decision-making

Animal approach-avoidance conflict paradigms have been used extensively to operationalize anxiety, quantify the effects of anxiolytic agents, and probe the neural basis of fear and anxiety. Results from human neuroimaging studies support that a frontal-striatal-amygdala neural circuitry is important for approach-avoidance learning. However, the neural basis of decision-making is much less clear in this context. Thus, we combined a recently developed human approach-avoidance paradigm with functional magnetic resonance imaging (fMRI) to identify neural substrates underlying approach-avoidance conflict decision-making. Fifteen healthy adults completed the approach-avoidance conflict (AAC) paradigm during fMRI. Analyses of variance were used to compare conflict to nonconflict (avoid-threat and approach-reward) conditions and to compare level of reward points offered during the decision phase. Trial-by-trial amplitude modulation analyses were used to delineate brain areas underlying decision-making in the context of approach/avoidance behavior. Conflict trials as compared to the nonconflict trials elicited greater activation within bilateral anterior cingulate cortex, anterior insula, and caudate, as well as right dorsolateral prefrontal cortex (PFC). Right caudate and lateral PFC activation was modulated by level of reward offered. Individuals who showed greater caudate activation exhibited less approach behavior. On a trial-by-trial basis, greater right lateral PFC activation related to less approach behavior. Taken together, results suggest that the degree of activation within prefrontal-striatal-insula circuitry determines the degree of approach versus avoidance decision-making. Moreover, the degree of caudate and lateral PFC activation related to individual differences in approach-avoidance decision-making. Therefore, the approach-avoidance conflict paradigm is ideally suited to probe anxiety-related processing differences during approach-avoidance decision-making.

Cortical thickness differences between bipolar depression and major depressive disorder

OBJECTIVES

Bipolar disorder (BD) is a psychiatric disorder with high morbidity and mortality that cannot be distinguished from major depressive disorder (MDD) until the first manic episode. A biomarker able to differentiate BD and MDD could help clinicians avoid risks of treating BD with antidepressants without mood stabilizers.

METHODS

Cortical thickness differences were assessed using magnetic resonance imaging in BD depressed patients (n = 18), MDD depressed patients (n = 56), and healthy volunteers (HVs) (n = 54). A general linear model identified clusters of cortical thickness difference between diagnostic groups.

RESULTS

Compared to the HV group, the BD group had decreased cortical thickness in six regions, after controlling for age and sex, located within the frontal and parietal lobes, and the posterior cingulate cortex. Mean cortical thickness changes in clusters ranged from 7.6 to 9.6% (cluster-wise p-values from 1.0 e-4 to 0.037). When compared to MDD, three clusters of lower cortical thickness in BD were identified that overlapped with clusters that differentiated the BD and HV groups. Mean cortical thickness changes in the clusters ranged from 7.5 to 8.2% (cluster-wise p-values from 1.0 e-4 to 0.023). The difference in cortical thickness was more pronounced when the subgroup of subjects with bipolar I disorder (BD-I) was compared to the MDD group.

CONCLUSIONS

Cortical thickness patterns were distinct between BD and MDD. These results are a step toward developing an imaging test to differentiate the two disorders.

rTMS in the treatment of drug addiction: an update about human studies

Drug addiction can be a devastating and chronic relapsing disorder with social, psychological, and physical consequences, and more effective treatment options are needed. Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive brain stimulation technique that has been assessed in a growing number of studies for its therapeutic potential in treating addiction. This review paper offers an overview on the current state of clinical research in treating drug addiction with rTMS. Because of the limited research in this area, all studies (including case reports) that evaluated the therapeutic use of rTMS in nicotine, alcohol, or illicit drug addiction were included in this review. Papers published prior to December 2012 were found through an NCBI PubMed search. A total of eleven studies were identified that met review criteria. There is nascent evidence that rTMS could be effective in reducing cocaine craving and nicotine and alcohol craving and consumption and might represent a potential therapeutic tool for treating addiction. Further studies are needed to identify the optimal parameters of stimulation for the most effective treatment of drug addiction, to improve our comprehension of the treatment neurophysiological effects, and to conduct rigorous, controlled efficacy studies with adequate power.

Decision making as a window on cognition

A decision is a commitment to a proposition or plan of action based on information and values associated with the possible outcomes. The process operates in a flexible timeframe that is free from the immediacy of evidence acquisition and the real time demands of action itself. Thus, it involves deliberation, planning, and strategizing. This Perspective focuses on perceptual decision making in nonhuman primates and the discovery of neural mechanisms that support accuracy, speed, and confidence in a decision. We suggest that these mechanisms expose principles of cognitive function in general, and we speculate about the challenges and directions before the field.

Human perceptual decision making: disentangling task onset and stimulus onset

The left dorsolateral prefrontal cortex (ldlPFC) has been highlighted as a key actor in human perceptual decision-making (PDM): It is theorized to support decision-formation independently of stimulus type or motor response. PDM studies however generally confound stimulus onset and task onset: when the to-be-recognized stimulus is presented, subjects know that a stimulus is shown and can set up processing resources-even when they do not know which stimulus is shown. We hypothesized that the ldlPFC might be involved in task preparation rather than decision-formation. To test this, we asked participants to report whether sequences of noisy images contained a face or a house within an experimental design that decorrelates stimulus and task onset. Decision-related processes should yield a sustained response during the task, whereas preparation-related areas should yield transient responses at its beginning. The results show that the brain activation pattern at task onset is strikingly similar to that observed in previous PDM studies. In particular, they contradict the idea that ldlPFC forms an abstract decision and suggest instead that its activation reflects preparation for the upcoming task. We further investigated the role of the fusiform face areas and parahippocampal place areas which are thought to be face and house detectors, respectively, that feed their signals to higher level decision areas. The response patterns within these areas suggest that this interpretation is unlikely and that the decisions about the presence of a face or a house in a noisy image might instead already be computed within these areas without requiring higher-order areas.

Non-invasive brain stimulation can induce paradoxical facilitation. Are these neuroenhancements transferable and meaningful to security services?

For ages, we have been looking for ways to enhance our physical and cognitive capacities in order to augment our security. One potential way to enhance our capacities may be to externally stimulate the brain. Methods of non-invasive brain stimulation (NIBS), such as repetitive transcranial magnetic stimulation (rTMS) and transcranial electrical stimulation (tES), have been recently developed to modulate brain activity. Both techniques are relatively safe and can transiently modify motor and cognitive functions outlasting the stimulation period. The purpose of this paper is to review data suggesting that NIBS can enhance motor and cognitive performance in healthy volunteers. We frame these findings in the context of whether they may serve security purposes. Specifically, we review studies reporting that NIBS induces paradoxical facilitation in motor (precision, speed, strength, acceleration endurance, and execution of daily motor task) and cognitive functions (attention, impulsive behavior, risk-taking, working memory, planning, and deceptive capacities). Although transferability and meaningfulness of these NIBS-induced paradoxical facilitations into real-life situations are not clear yet, NIBS may contribute at improving training of motor and cognitive functions relevant for military, civil, and forensic security services. This is an enthusiastic perspective that also calls for fair and open debates on the ethics of using NIBS in healthy individuals to enhance normal functions.

Deep transcranial magnetic stimulation for the treatment of pathological gambling

Five pathological gamblers received deep transcranial magnetic stimulation (DTMS). Evaluations included rating scales and collateral anamnesis. Despite initial improvement in ratings, collateral anamnesis demonstrated failure to respond. DTMS to the pre-frontal cortex using an H1 coil was an ineffective treatment. Our study is preliminary, and additional studies are required.

A supramodal accumulation-to-bound signal that determines perceptual decisions in humans

In theoretical accounts of perceptual decision-making, a decision variable integrates noisy sensory evidence and determines action through a boundary-crossing criterion. Signals bearing these very properties have been characterized in single neurons in monkeys, but have yet to be directly identified in humans. Using a gradual target detection task, we isolated a freely evolving decision variable signal in human subjects that exhibited every aspect of the dynamics observed in its single-neuron counterparts. This signal could be continuously tracked in parallel with fully dissociable sensory encoding and motor preparation signals, and could be systematically perturbed mid-flight during decision formation. Furthermore, we found that the signal was completely domain general: it exhibited the same decision-predictive dynamics regardless of sensory modality and stimulus features and tracked cumulative evidence even in the absence of overt action. These findings provide a uniquely clear view on the neural determinants of simple perceptual decisions in humans.

Single-trial analysis of neuroimaging data: inferring neural networks underlying perceptual decision-making in the human brain

Advances in neural signal and image acquisition as well as in multivariate signal processing and machine learning are enabling a richer and more rigorous understanding of the neural basis of human decision-making. Decision-making is essentially characterized behaviorally by the variability of the decision across individual trials--e.g., error and response time distributions. To infer the neural processes that govern decision-making requires identifying neural correlates of such trial-to-trial behavioral variability. In this paper, we review efforts that utilize signal processing and machine learning to enable single-trial analysis of neural signals acquired while subjects perform simple decision-making tasks. Our focus is on neuroimaging data collected noninvasively via electroencephalograpy (EEG) and functional magnetic resonance imaging (fMRI). We review the specific framework for extracting decision-relevant neural components from the neuroimaging data, the goal being to analyze the trial-to-trial variability of the neural signal along these component directions and to relate them to elements of the decision-making process. We review results for perceptual decision-making and discrimination tasks, including paradigms in which EEG variability is used to inform an fMRI analysis. We discuss how single-trial analysis reveals aspects of the underlying decision-making networks that are unobservable using traditional trial-averaging methods.

Brain stimulation methods to treat tobacco addiction

BACKGROUND

Tobacco smoking is the leading cause of preventable deaths worldwide, but many smokers are simply unable to quit. Psychosocial and pharmaceutical treatments have shown modest results on smoking cessation rates, but there is an urgent need to develop treatments with greater efficacy. Brain stimulation methods are gaining increasing interest as possible addiction therapeutics.

OBJECTIVES

The purpose of this paper is to review the studies that have evaluated brain stimulation techniques on tobacco addiction, and discuss future directions for research in this novel area of addiction interventions.

METHODS

Electronic and manual literature searches identified fifteen studies that administered repetitive transcranial magnetic stimulation (rTMS), cranial electrostimulation (CES), transcranial direct current stimulation (tDCS) or deep brain stimulation (DBS).

RESULTS

rTMS was found to be the most well studied method with respect to tobacco addiction. Results indicate that rTMS and tDCS targeted to the dorsolateral prefrontal cortex (DLPFC) were the most efficacious in reducing tobacco cravings, an effect that may be mediated through the brain reward system involved in tobacco addiction. While rTMS was shown to reduce consumption of cigarettes, as yet no brain stimulation technique has been shown to significantly increase abstinence rates. It is possible that the therapeutic effects of rTMS and tDCS may be improved by optimization of stimulation parameters and increasing the duration of treatment.

CONCLUSION

Although further studies are needed to confirm the ability of brain stimulation methods to treat tobacco addiction, this review indicates that rTMS and tDCS both represent potentially novel treatment modalities.

Active encoding of decisions about stimulus absence in primate prefrontal cortex neurons

Judging the presence or absence of a stimulus is likely the most basic perceptual decision. A fundamental difference of detection tasks in contrast to discrimination tasks is that only the stimulus presence decision can be inferred from sensory evidence, whereas the alternative decision about stimulus absence lacks sensory evidence by definition. Detection decisions have been studied in an intentional, action-based framework, in which decisions were regarded as intentions to pursue particular actions. These studies have found that only stimulus-present decisions are actively encoded by neurons, whereas the decision about the absence of a stimulus does not affect default neuronal responses. We tested whether this processing mechanism also holds for abstract detection decisions that are dissociated from motor preparation. We recorded single-neuron activity from the prefrontal cortex (PFC) of monkeys performing a visual detection task that forced a report-independent decision. We not only found neurons that actively encoded the subjective decision of monkeys about the presence of a stimulus, but also cells responding actively for the decision about the absence of stimuli. These results suggest that abstract detection decisions are processed in a different way compared with the previously reported action-based decisions. In a report-independent framework, neuronal networks seem to generate a second set of neurons actively encoding the absence of sensory stimulation, thus translating decisions into abstract categories. This mechanism may allow the brain to "buffer" a decision in a nonmovement-related framework.

Neural signatures of economic parameters during decision-making: a functional MRI (FMRI), electroencephalography (EEG) and autonomic monitoring study

Adaptive behaviour requires an ability to obtain rewards by choosing between different risky options. Financial gambles can be used to study effective decision-making experimentally, and to distinguish processes involved in choice option evaluation from outcome feedback and other contextual factors. Here, we used a paradigm where participants evaluated 'mixed' gambles, each presenting a potential gain and a potential loss and an associated variable outcome probability. We recorded neural responses using autonomic monitoring, electroencephalography (EEG) and functional neuroimaging (fMRI), and used a univariate, parametric design to test for correlations with the eleven economic parameters that varied across gambles, including expected value (EV) and amount magnitude. Consistent with behavioural economic theory, participants were risk-averse. Gamble evaluation generated detectable autonomic responses, but only weak correlations with outcome uncertainty were found, suggesting that peripheral autonomic feedback does not play a major role in this task. Long-latency stimulus-evoked EEG potentials were sensitive to expected gain and expected value, while alpha-band power reflected expected loss and amount magnitude, suggesting parallel representations of distinct economic qualities in cortical activation and central arousal. Neural correlates of expected value representation were localized using fMRI to ventromedial prefrontal cortex, while the processing of other economic parameters was associated with distinct patterns across lateral prefrontal, cingulate, insula and occipital cortices including default-mode network and early visual areas. These multimodal data provide complementary evidence for distributed substrates of choice evaluation across multiple, predominantly cortical, brain systems wherein distinct regions are preferentially attuned to specific economic features. Our findings extend biologically-plausible models of risky decision-making while providing potential biomarkers of economic representations that can be applied to the study of deficits in motivational behaviour in neurological and psychiatric patients.

Repetitive transcranial magnetic stimulation and drug addiction

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation technique that is now being tested for its ability to treat addiction. This review discusses current research approaches and results of studies which measured the therapeutic use of rTMS to treat tobacco, alcohol and illicit drug addiction. The research in this area is limited and therefore all studies evaluating the therapeutic use of rTMS in tobacco, alcohol or illicit drug addiction were retained including case studies through NCBI PubMed ( http://www.ncbi.nlm.nih.gov ) and manual searches. A total of eight studies were identified that examined the ability of rTMS to treat tobacco, alcohol and cocaine addiction. The results of this review indicate that rTMS is effective in reducing the level of cravings for smoking, alcohol, and cocaine when applied at high frequencies to the dorsolateral prefrontal cortex (DLPFC). Furthermore, these studies suggest that repeated sessions of high frequency rTMS over the DLPFC may be most effective in reducing the level of smoking and alcohol consumption. Although work in this area is limited, this review indicates that rTMS is a promising modality for treating drug addiction.

Flexible interpretation of a decision rule by supplementary eye field neurons

Since the environment is in constant flux, decision-making capabilities of the brain must be rapid and flexible. Yet in sensory motion processing pathways of the primate brain where decision making has been extensively studied, the flexibility of neurons is limited by inherent selectivity to motion direction and speed. The supplementary eye field (SEF), an area involved in decision making on moving stimuli, is not strictly a sensory or motor structure, and hence may not suffer such limitations. Here we test whether neurons in the SEF can flexibly interpret the rule of a go/nogo task when the decision boundary in the task changes with each trial. The task rule specified that the animal pursue a moving target with its eyes if and when the target entered a visible zone. The size of the zone was changed from trial to trial in order to shift the decision boundary, and thereby assign different go/nogo significance to the same motion trajectories. Individual SEF neurons interpreted the rule appropriately, signaling go or nogo in compliance with the rule and not the direction of motion. The results provide the first evidence that individual neurons in frontal cortex can flexibly interpret a rule that governs the decision to act.

Category learning in the brain

The ability to group items and events into functional categories is a fundamental characteristic of sophisticated thought. It is subserved by plasticity in many neural systems, including neocortical regions (sensory, prefrontal, parietal, and motor cortex), the medial temporal lobe, the basal ganglia, and midbrain dopaminergic systems. These systems interact during category learning. Corticostriatal loops may mediate recursive, bootstrapping interactions between fast reward-gated plasticity in the basal ganglia and slow reward-shaded plasticity in the cortex. This can provide a balance between acquisition of details of experiences and generalization across them. Interactions between the corticostriatal loops can integrate perceptual, response, and feedback-related aspects of the task and mediate the shift from novice to skilled performance. The basal ganglia and medial temporal lobe interact competitively or cooperatively, depending on the demands of the learning task.

Transcranial direct current stimulation facilitates decision making in a probabilistic guessing task

In a random sequence of binary events where one alternative occurs more often than the other, humans tend to guess which of the two alternatives will occur next by trying to match the frequencies of previous occurrences. Based on split-brain and unilaterally damaged patients' performances, it has been proposed that the left hemisphere (LH) tends to match the frequencies, while the right hemisphere (RH) tends toward maximizing and always choosing the most frequent alternative. The current study used transcranial direct current stimulation (tDCS) to test this hemispheric asymmetry hypothesis by stimulating the dorsolateral prefrontal cortex of each hemisphere and simultaneously inhibiting the corresponding region in the homotopic hemisphere, while participants were engaged in a probabilistic guessing task. Results showed no difference in strategy between the three groups (RH anodal/LH cathodal, LH anodal/RH cathodal, no stimulation) as participants predominantly matched the frequencies of the two alternatives. However, when anodal tDCS was applied to the LH and cathodal tDCS applied to the RH, participants became quicker to select the most frequent alternative. This finding is in line with previous evidence on the involvement of the LH in probabilistic learning and reasoning and adds to a number of demonstrations of anodal tDCS leading to some behavioral enhancement or change in bias.

Similarity, typicality, and category-level matching of morphed outlines of everyday objects

During visual object categorisation, a match must be found between the input image and stored information about basic-level categories. Graf [2002 Form, Space and Object (Berlin: Wissenschaftlicher Verlag Berlin)] suggested the involvement of analogue transformational, shape-changing processes in aligning the memory representation of the category with the perceptual representation of the current stimulus. Here we compare the predictions of alignment models with those of exemplar-based models, using morphing between four exemplar outlines within each of eleven categories. Overall, with increasing transformational distance between two exemplars of the same category, reaction times to decide whether they belong to the same category in a sequential matching paradigm increased, while rated similarity between the two exemplars decreased. However, in contrast to alignment accounts, exemplar-based accounts can correctly predict the observed dissociation between typicality and categorisation time, and allow the observed deviations from sequential additivity and nonlinear relations between transformational distance and rated similarity. Discussion of integrations of exemplar-based theories with neglected processes, such as information accumulation, response competition, response priming, and gain-modulation leads to a view of the recognition process from input to response, which increases the validity and scope of modern exemplar-based categorisation and recognition models.

Increased dorsolateral prefrontal cortex activation in obese children during observation of food stimuli

OBJECTIVE

Food cues yield different patterns of brain activation in obese compared with normal-weight adults in prefrontal and limbic/paralimbic areas. For children, no mapping studies comparing representation sites for food and other stimuli between obese and normal-weight subjects are available.

DESIGN

We used a cross-sectional design of two age-matched subject groups to investigate differences in brain activation in response to visually presented food, pleasant, and neutral pictures between obese/overweight and normal children.

SUBJECTS

22 overweight/obese children were compared with 22 normal-weight children.

MEASUREMENTS

Functional magnetic resonance imaging (of the whole head during perception of visually presented stimuli), psychological testing, and psychophysical measures of heart rate deceleration were assessed.

RESULTS

Obese children showed higher activation of the dorsolateral prefrontal cortex (DLPFC) in response to food pictures. In addition, DLPFC activation was negatively correlated with self-esteem. In contrast, normal-weight children showed higher activation of the caudate and hippocampus specific to food pictures, and of the anterior cingulate cortex and thalamus to visual cues in general. In response to food stimuli, obese children showed a heart rate deceleration correlating positively with activation of the ventrolateral prefrontal cortex.

CONCLUSION

Obese children react to food stimuli with increased prefrontal activation, which might be associated with increased inhibitory control.

Neural computations underlying action-based decision making in the human brain

Action-based decision making involves choices between different physical actions to obtain rewards. To make such decisions the brain needs to assign a value to each action and then compare them to make a choice. Using fMRI in human subjects, we found evidence for action-value signals in supplementary motor cortex. Separate brain regions, most prominently ventromedial prefrontal cortex, were involved in encoding the expected value of the action that was ultimately taken. These findings differentiate two main forms of value signals in the human brain: those relating to the value of each available action, likely reflecting signals that are a precursor of choice, and those corresponding to the expected value of the action that is subsequently chosen, and therefore reflecting the consequence of the decision process. Furthermore, we also found signals in the dorsomedial frontal cortex that resemble the output of a decision comparator, which implicates this region in the computation of the decision itself.

Biases and optimality of sensory-motor and cognitive decisions

I review a variety of behavioral studies directed at understanding how probability and value information is represented in motor and cognitive tasks. Subjects in (cognitive) decision-making tasks often misrepresent the frequency of rare events and typically fail to maximize expected gain. In contrast, subjects in mathematically equivalent movement tasks are generally found to be very good at choosing motor strategies that come close to maximizing expected gain. I discuss the differences between the sources of uncertainty for decisions in the motor and cognitive domain and summarize experimental evidence about how information about uncertainty is acquired in motor and cognitive decision tasks. Finally, I briefly review the evidence concerning the neural coding of probability, expected gain, and other information in decision-making tasks.

Release of premotor activity after repetitive transcranial magnetic stimulation of prefrontal cortex

In the present study we aimed to explore by means of repetitive transcranial magnetic stimulation (rTMS) the reciprocal influences between prefrontal cortex (PFC) and premotor cortex (PMC). Subjects were asked to observe on a computer monitor different pictures representing manipulations of different kind of tools. They had to produce a movement (go condition) or to keep the resting position (no-go condition) at the appearance of different cue signals represented by different colors shown alternatively on the hands manipulating the tools or on the picture background. Motor evoked potentials (MEPs) were collected at the offset of the visual stimuli before and after a 10 minute, 1 Hz rTMS train applied to the dorsolateral PFC (Experiment 1), to the PMC (Experiment 2) or to the primary motor cortex (Experiment 3). Following rTMS to the PFC, MEPs increased in the go condition when the cue for the go command was presented on the hand. In contrast, following rTMS to the PMC, in the same condition, MEPs were decreased. rTMS to the primary motor cortex did not produce any modulation. Results are discussed according to the presence of a visual-motor matching system in the PMC and to the role of the PFC in the attention-related processes. We hypothesize that the perceptual analysis for action selection within the PFC was modulated by rTMS and its temporary functional inactivation in turn influenced the premotor areas for motor programming.

Repeated high-frequency transcranial magnetic stimulation over the dorsolateral prefrontal cortex reduces cigarette craving and consumption

AIMS

To evaluate the effect of repeated high-frequency transcranial magnetic stimulation (rTMS) of the left dorsolateral prefrontal cortex (DLPFC), combined with either smoking or neutral cues, on cigarette consumption, dependence and craving.

DESIGN

Participants were divided randomly to real and sham stimulation groups. Each group was subdivided randomly into two subgroups presented with either smoking-related or neutral pictures just before the daily TMS intervention. Ten daily rTMS sessions were applied every week-day and then a maintenance phase was conducted in which rTMS sessions were less frequent.

SETTING

Single-site, out-patient, randomized, double-blind, sham-controlled.

PARTICIPANTS

Forty-eight chronic smokers who smoked at least 20 cigarettes per day and were motivated to quit smoking. Healthy males and females were recruited from the general population using advertisements in newspapers and on internet websites.

INTERVENTION

Ten daily rTMS sessions were administered using a standard figure-8 coil over the DLPFC. Stimulation included 20 trains/day at 100% of motor threshold. Each train consisted of 50 pulses at 10 Hz with an inter-train interval of 15 seconds.

MEASUREMENTS

Cigarette consumption was evaluated objectively by measuring cotinine levels in urine samples and subjectively by participants' self-reports. Dependence and craving were evaluated by standard questionnaires.

FINDINGS

Ten daily rTMS sessions over the DLPFC reduced cigarette consumption and nicotine dependence. Furthermore, treatment blocked the craving induced by daily presentation of smoking-related pictures. However, these effects tended to dissipate over time.

CONCLUSIONS

Multiple high-frequency rTMS of the DLPFC can attenuate nicotine craving.

Neural correlates of spontaneous percept switches in ambiguous stimuli: an event-related functional magnetic resonance imaging study

When ambiguous visual stimuli are being looked at, perception alternates spontaneously between two competing interpretations of the same sensory input. One major issue in understanding the underlying neural process is whether spontaneous percept switches result from fluctuations at the level of sensory processes or whether they are initiated by higher-order areas. To further study this question, we developed an ambiguous apparent motion paradigm that specifically focused on the generation of percept switches. The percept switches occurred either spontaneously or were experimentally triggered. The differential analysis of spontaneous and triggered percept switches was aimed at disentangling the causes and effects of percept switches. Spontaneous percept switches were associated with stronger activations at the right occipitotemporal junction, whereas prefrontal, superior temporal and inferior parietal regions showed greater activations during experimentally triggered percept switches. We propose that complex networks including both sensory and higher-order areas are involved in percept switches, whereas stimulus-specific sensory processes are crucial for the initiation of spontaneous percept switches.

Sensory-motor mechanisms in human parietal cortex underlie arbitrary visual decisions

The neural mechanism underlying simple perceptual decision-making in monkeys has been recently conceptualized as an integrative process in which sensory evidence supporting different response options accumulates gradually over time. For example, intraparietal neurons accumulate motion information in favor of a specific oculomotor choice over time. It is unclear, however, whether this mechanism generalizes to more complex decisions that are based on arbitrary stimulus-response associations. In a task requiring arbitrary association of visual stimuli (faces or places) with different actions (eye or hand-pointing movements), we found that activity of effector-specific regions in human posterior parietal cortex reflected the 'strength' of the sensory evidence in favor of the preferred response. These regions did not respond to sensory stimuli per se but integrated sensory evidence toward the decision outcome. We conclude that even arbitrary decisions can be mediated by sensory-motor mechanisms that are completely triggered by contextual stimulus-response associations.

fMRI evidence for a dual process account of the speed-accuracy tradeoff in decision-making

BACKGROUND

The speed and accuracy of decision-making have a well-known trading relationship: hasty decisions are more prone to errors while careful, accurate judgments take more time. Despite the pervasiveness of this speed-accuracy trade-off (SAT) in decision-making, its neural basis is still unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Using functional magnetic resonance imaging (fMRI) we show that emphasizing the speed of a perceptual decision at the expense of its accuracy lowers the amount of evidence-related activity in lateral prefrontal cortex. Moreover, this speed-accuracy difference in lateral prefrontal cortex activity correlates with the speed-accuracy difference in the decision criterion metric of signal detection theory. We also show that the same instructions increase baseline activity in a dorso-medial cortical area involved in the internal generation of actions.

CONCLUSIONS/SIGNIFICANCE

These findings suggest that the SAT is neurally implemented by modulating not only the amount of externally-derived sensory evidence used to make a decision, but also the internal urge to make a response. We propose that these processes combine to control the temporal dynamics of the speed-accuracy trade-off in decision-making.

Control over conflict during movement preparation: role of posterior parietal cortex

Flexible behavior in humans often requires that rapid choices be made between conflicting action plans. Although much attention has focused on prefrontal regions, little is understood about the contribution of parietal cortex under situations of response conflict. Here we show that right parietal damage associated with spatial neglect leads to paradoxical facilitation (speeding) of rightward movements in the presence of conflicting leftward response plans. These findings indicate a critical role for parietal regions in action planning when there is response competition. In contrast, patients with prefrontal damage have an augmented cost of conflict for both leftward and rightward movements. The results suggest involvement of two independent systems in situations of response conflict, with right parietal cortex being a crucial site for automatic activation of competing motor plans and prefrontal regions acting independently to inhibit action plans irrelevant to current task goals.

Physiology and pathology of eye–head coordination

Human head movement control can be considered as part of the oculomotor system since the control of gaze involves coordination of the eyes and head. Humans show a remarkable degree of flexibility in eye-head coordination strategies, nonetheless an individual will often demonstrate stereotypical patterns of eye-head behaviour for a given visual task. This review examines eye-head coordination in laboratory-based visual tasks, such as saccadic gaze shifts and combined eye-head pursuit, and in common tasks in daily life, such as reading. The effect of the aging process on eye-head coordination is then reviewed from infancy through to senescence. Consideration is also given to how pathology can affect eye-head coordination from the lowest through to the highest levels of oculomotor control, comparing conditions as diverse as eye movement restrictions and schizophrenia. Given the adaptability of the eye-head system we postulate that this flexible system is under the control of the frontal cortical regions, which assist in planning, coordinating and executing behaviour. We provide evidence for this based on changes in eye-head coordination dependant on the context and expectation of presented visual stimuli, as well as from changes in eye-head coordination caused by frontal lobe dysfunction.

Toward an understanding of the cerebral substrates of woman's orgasm

The way women experience orgasm is of interest to scientists, clinicians, and laypeople. Whereas the origin and the function of a woman's orgasm remains controversial, the current models of sexual function acknowledge a combined role of central (spinal and cerebral) and peripheral processes during orgasm experience. At the central level, although it is accepted that the spinal cord drives orgasm, the cerebral involvement and cognitive representation of a woman's orgasm has not been extensively investigated. Important gaps in our knowledge remain. Recently, the astonishing advances of neuroimaging techniques applied in parallel with a neuropsychological approach allowed the unravelling of specific functional neuroanatomy of a woman's orgasm. Here, clinical and experimental findings on the cortico-subcortical pathway of a woman's orgasm are reviewed and compared with the neural basis of a man's orgasm. By defining the specific brain areas that sustain the assumed higher-order representation of a woman's orgasm, this review provides a foundation for future studies. The next challenge of functional imaging and neuropsychological studies is to understand the hierarchical interactions between these multiple cortical areas, not only with a correlation analysis but also with high spatio-temporal resolution techniques demonstrating the causal necessity, the temporal time course and the direction of the causality. Further studies using a multi-disciplinary approach are needed to identify the spatio-temporal dynamic of a woman's orgasm, its dysfunctions and possible new treatments.

Dynamics of oscillatory activity during auditory decision making

Perceptual decision making requires the comparison and integration of sensory evidence to generate a behavioral response. We used magnetoencephalography to investigate the temporal dynamics of decision making during an auditory task that required forced-choice decisions about whether a pair of syllables S1 and S2 differed either in their acoustic patterns or in the perceived position of their sound sources. Conditions with easy and difficult decisions were created by varying the similarity of S1 and S2. Statistical probability mapping showed enhanced gamma-band activity (GBA) over posterior parietal cortex for spatial and over left inferior frontal cortex for pattern changes (at approximately 120 to 220 ms after S2 onset). Activations were stronger for easy than difficult decisions. GBA over dorsolateral prefrontal cortex was more pronounced at approximately 280 to 430 ms for easy than difficult decisions regardless of type of change, possibly reflecting decision-relevant networks that integrate information from higher sensory areas representing the perceptual alternatives. Sensorimotor beta desynchronization as a measure of motor preparation peaked at approximately 460 ms for easy and at approximately 520 ms for difficult decisions, thus reflecting the reaction time difference between both conditions. In summary, the analysis of oscillatory activity in magnetoencephalogram served to elucidate the temporal dynamics of perceptual decision making in humans.