Altered processing of sensorimotor feedback in schizophrenia

Schizophrenia is characterized by an altered sense of the reality, associated with hallucinations and delusions. Some theories suggest that schizophrenia is related to a deficiency of the system that generates information about the sensory consequences of the actions realized by the subject. This system monitors the reafferent information resulting from an action and allows its anticipation. In the present study, we examined visual-event-related potentials (ERPs) generated by a sensorimotor task in 15 patients with schizophrenia and 15 normal controls. The visual feedback from hand movements performed by the subjects was experimentally distorted. Behavioral results showed that patients were impaired in recognizing their own movements. The ERP signal in patients also differed from those of control subjects. In patients, the ERP waveform was affected during the early part of the response (200 ms). This early effect in schizophrenic patients reveals a modified processing of the visual consequence of their actions.     

The neural basis of hallucinations and delusions

Schizophrenia is a biologically based disorder characterised by false perceptions (hallucinations) and false beliefs (delusions). The underlying physiological cause of these mental abnormalities remains unknown. There is increasing evidence that one class of symptom, the 'made experiences' including delusions of alien control and thought insertion, is associated with abnormalities in the mechanism that predicts the outcome of intended actions (the forward model). For these patients active movements feel like passive movements. As a result these patients do not feel in control of their actions. However, comparison with various neurological disorders, such as those associated with parietal lobe lesions, suggest that this abnormal experience is not sufficient to explain the feeling that some other agent is controlling is one's actions. Preliminary evidence suggests that patients with schizophrenia have an exaggerated sense of agency. In combination with the feeling of not being in control, this exaggerated sense of agency could explain delusions of alien control in which the patient attributes his own actions to another agent. Little is yet know about the neural basis of the predictive mechanisms that create the feeling that we are in control of our movements. Such prediction requires integration of information about intended movements generated in frontal cortex with sensory processing in posterior regions of the brain. Measures of functional connectivity suggest that long-range interactions between frontal and posterior regions are abnormally reduced in patients with schizophrenia. Further research is needed to explore the precise involvement of long-range connections in the mechanisms of forward modelling.     

The cerebellum updates predictions about the visual consequences of one's behavior

Each action has sensory consequences that need to be distinguished from sensations arising from the environment. This is accomplished by the comparing of internal predictions about these consequences with the actual afference, thereby isolating the afferent component that is self-produced. Because the sensory consequences of actions vary as a result of changes of the effector's efficacy, internal predictions need to be updated continuously and on a short time scale. Here, we tested the hypothesis that this updating of predictions about the sensory consequences of actions is mediated by the cerebellum, a notion that parallels the cerebellum's role in motor learning. Patients with cerebellar lesions and their matched controls were equally able to detect experimental modifications of visual feedback about their pointing movements. When such feedback was constantly rotated, both groups instantly attributed the visual feedback to their own actions. However, in interleaved trials without actual feedback, patients did no longer account for this feedback rotation--neither perceptually nor with respect to motor performance. Both deficits can be explained by an impaired updating of internal predictions about the sensory consequences of actions caused by cerebellar pathology. Thus, the cerebellum guarantees both precise performance and veridical perceptual interpretation of actions.     

Self-awareness and action

In this review we discuss how we are aware that actions are self-generated. We review behavioural data that suggest that a prediction of the sensory consequences of movement might be used to label actions and their consequences as self-generated. We also describe recent functional neuroimaging experiments and studies of neurological and psychiatric patients, which suggest that the parietal cortex plays a crucial role in the awareness of action.     

Granger causality mapping during joint actions reveals evidence for forward models that could overcome sensory-motor delays

Studies investigating joint actions have suggested a central role for the putative mirror neuron system (pMNS) because of the close link between perception and action provided by these brain regions [1], [2], [3]. In contrast, our previous functional magnetic resonance imaging (fMRI) experiment demonstrated that the BOLD response of the pMNS does not suggest that it directly integrates observed and executed actions during joint actions [4]. To test whether the pMNS might contribute indirectly to the integration process by sending information to brain areas responsible for this integration (integration network), here we used Granger causality mapping (GCM) [5]. We explored the directional information flow between the anterior sites of the pMNS and previously identified integrative brain regions. We found that the left BA44 sent more information than it received to both the integration network (left thalamus, right middle occipital gyrus and cerebellum) and more posterior nodes of the pMNS (BA2). Thus, during joint actions, two anatomically separate networks therefore seem effectively connected and the information flow is predominantly from anterior to posterior areas of the brain. These findings suggest that the pMNS is involved indirectly in joint actions by transforming observed and executed actions into a common code and is part of a generative model that could predict the future somatosensory and visual consequences of observed and executed actions in order to overcome otherwise inevitable neural delays.     

Rôle du sens de l’effort dans le syndrome d’influence

Centrally generated signals from premotor areas play a key role in voluntary muscle force perception. Indeed, sensations of effort, rather than sensations of intramuscular tension, make it possible to evaluate the intensity of willed muscle forces. We suggest that the sense of effort is involved in agency, the cognitive process by which one is aware of one’s actions. We argue that effort awareness accompanies each action and is the key component of the feeling of will. In delusions of alien control, patients with schizophrenia do not recognize some of their acts as their own and are convinced that they are under the control of someone else. Some experimental data suggest that delusions of control are related to an altered awareness of effort and an exaggerated awareness of afferent neural information, caused by neurological disorders in the frontal and parietal lobes. This impairment could lead to the inability to identify the author of an action. In this pathological condition, the cerebral state coding for “I intend to act” might move toward the state coding for “someone else intends to act”, even in the absence of another agent.     

By the teeth of their skin, cavefish find their way

Teeth and skin teeth (denticles), collectively named odontodes, are usually associated with the physical roles of cutting, protection or drag reduction in fishes [1,2]. These structures are composed of a soft pulp surrounded by dentine and covered by a mineralized substance such as enamel [3]. Odontodes arise from neural crest cells and epithelium and are often innervated [1-3]. However, little is known about their possible sensory function. Here, we demonstrate for the first time a mechanosensory role for denticles in a cavefish endemic to a fast water flow cave. All fishes gather hydrodynamic information via specialized sense organs called neuromasts [4-6]. Some fishes are especially attentive to such type of information [5] and until now hypertrophy of the neuromast system has been reported as the main constructive sensory adaptation in cavefishes [6,7]. We expect that the mechanosensory nature of denticles highlighted in this cave fish species might reflect a widespread sensory role for these structures in other animals.     

Brain mechanisms associated with top-down processes in perception.

Perception arises through an interaction between sensory input and prior knowledge. We propose that at least two brain areas are required for such an interaction: the ''site'' where analysis of afferent signals occurs and the ''source'' which applies the relevant prior knowledge. In the human brain, functional imaging studies have demonstrated that selective attention modifies activity in early visual processing areas specific to the attended feature. Early processing areas are also modified when prior knowledge permits a percept to emerge from an otherwise meaningless stimulus. Sources of this modification have been identified in parietal cortex and in prefrontal cortex. Modification of early processing areas also occurs on the basis of prior knowledge about the predicted sensory effects of the subject''s own actions. Activity associated with mental imagery resembles that associated with response preparation (for motor imagery) and selective attention (for sensory imagery) suggesting that mental imagery reflects the effects of prior knowledge on sensory processing areas in the absence of sensory input. Damage to sensory processing areas can lead to a form of sensory hallucination which seems to arise from the interaction of prior knowledge with random sensory activity. In contrast, hallucinations associated with schizophrenia may arise from a failure of prior knowledge about motor intentions to modify activity in relevant sensory areas. When functioning normally, this mechanism permits us to distinguish our own actions from those of independent agents in the outside world. Failure to make this distinction correctly may account for the strong association between hallucinations and paranoid delusions in schizophrenia; the patient not only hears voices, but attributes (usually hostile) intentions to these voices.     

Phenomenological and neurocognitive perspectives on delusions: A critical overview

There is considerable overlap between phenomenological and neurocognitive perspectives on delusions. In this paper, we first review major phenomenological accounts of delusions, beginning with Jaspers’ ideas regarding incomprehensibility, delusional mood, and disturbed “cogito” (basic, minimal, or core self‐experience) in what he termed “delusion proper” in schizophrenia. Then we discuss later studies of decontextualization and delusional mood by Matussek, changes in self and world in delusion formation according to Conrad's notions of “apophany” and “anastrophe”, and the implications of ontological transformations in the felt sense of reality in some delusions. Next we consider consistencies between: a) phenomenological models stressing minimal‐self (ipseity) disturbance and hyperreflexivity in schizophrenia, and b) recent neurocognitive models of delusions emphasizing salience dysregulation and prediction error. We voice reservations about homogenizing tendencies in neurocognitive explanations of delusions (the “paranoia paradigm”), given experiential variations in states of delusion. In particular we consider shortcomings of assuming that delusions necessarily or always involve “mistaken beliefs” concerning objective facts about the world. Finally, we offer some suggestions regarding possible neurocognitive factors. Current models that stress hypersalience (banal stimuli experienced as strange) might benefit from considering the potential role of hyposalience in delusion formation. Hyposalience – associated with experiencing the strange as if it were banal, and perhaps with activation of the default mode network – may underlie a kind of delusional derealization and an “anything goes” attitude. Such an attitude would be conducive to delusion formation, yet differs significantly from the hypersalience emphasized in current neurocognitive theories.     

Believing is seeing: expectations alter visual awareness

Expectations have been shown to be powerful modulators of pain [1] and emotion [2] in placebo studies. In such experiments, expectations are induced by instructions combined with manipulation of the sensory experience that is unknown to the subjects. After an expectation learning phase where a painful stimulation is surreptitiously lowered following placebo application, the placebo effectively reduces subjective pain intensity in a subsequent test phase [3]. The strength of this placebo effect is closely related to the induced expectation [4]. Here, we asked whether this powerful cognitive bias reflects a general property of sensory information processing and tested whether the contents of visual awareness could be altered by a placebo-like expectation manipulation. We found a dramatic effect of experimentally induced expectations on the perception of an ambiguous visual motion stimulus. This shows that expectations have a strong and general influence on our experience of the sensory input independently of its specific type and content.     

Influence of uncertainty and surprise on human corticospinal excitability during preparation for action

Actions are guided by prior sensory information [1-10], which is inherently uncertain. However, how the motor system is sculpted by trial-by-trial content of current sensory information remains largely unexplored. Previous work suggests that conditional probabilities, learned under a particular context, can be used preemptively to influence the output of the motor system [11-14]. To test this we used transcranial magnetic stimulation (TMS) to read out corticospinal excitability (CSE) during preparation for action in an instructed delay task [15, 16]. We systematically varied the uncertainty about an impending action by changing the validity of the instructive visual cue. We used two information-theoretic quantities to predict changes in CSE, prior to action, on a trial-by-trial basis: entropy (average uncertainty) and surprise (the stimulus-bound information conveyed by a visual cue) [17-19]. Our data show that during preparation for action, human CSE varies according to the entropy and surprise conveyed by visual events guiding action. CSE increases on trials with low entropy about the impending action and low surprise conveyed by an event. Commensurate effects were observed in reaction times. We suggest that motor output is biased according to contextual probabilities that are represented dynamically in the brain.     

Mushroom Bodies Regulate Habit Formation in Drosophila

To make good decisions, we evaluate past choices to guide later decisions. In most situations, we have the opportunity to simultaneously learn about both the consequences of our choice (i.e., operantly) and the stimuli associated with correct or incorrect choices (i.e., classically) [1]. Interestingly, in many species, including humans, these learning processes occasionally lead to irrational decisions [2]. An extreme case is the habitual drug user consistently administering the drug despite the negative consequences, but we all have experience with our own, less severe habits. The standard animal model employs a combination of operant and classical learning components to bring about habit formation in rodents [3] and [4]. After extended training, these animals will press a lever even if the outcome associated with lever-pressing is no longer desired [5]. In this study, experiments with wild-type and transgenic flies revealed that a prominent insect neuropil, the mushroom bodies (MBs), regulates habit formation in flies by inhibiting the operant learning system when a predictive stimulus is present. This inhibition enables generalization of the classical memory and prevents premature habit formation. Extended training in wild-type flies produced a phenocopy of MB-impaired flies, such that generalization was abolished and goal-directed actions were transformed into habitual responses.     

No increased circular inference in adults with high levels of autistic traits or autism

Autism spectrum disorders have been proposed to arise from impairments in the probabilistic integration of prior knowledge with sensory inputs. Circular inference is one such possible impairment, in which excitation-to-inhibition imbalances in the cerebral cortex cause the reverberation and amplification of prior beliefs and sensory information. Recent empirical work has associated circular inference with the clinical dimensions of schizophrenia. Inhibition impairments have also been observed in autism, suggesting that signal reverberation might be present in that condition as well. In this study, we collected data from 21 participants with self-reported diagnoses of autism spectrum disorders and 155 participants with a broad range of autistic traits in an online probabilistic decision-making task (the fisher task). We used previously established Bayesian models to investigate possible associations between autistic traits or autism and circular inference. There was no correlation between prior or likelihood reverberation and autistic traits across the whole sample. Similarly, no differences in any of the circular inference model parameters were found between autistic participants and those with no diagnosis. Furthermore, participants incorporated information from both priors and likelihoods in their decisions, with no relationship between their weights and psychiatric traits, contrary to what common theories for both autism and schizophrenia would suggest. These findings suggest that there is no increased signal reverberation in autism, despite the known presence of excitation-to-inhibition imbalances. They can be used to further contrast and refine the Bayesian theories of schizophrenia and autism, revealing a divergence in the computational mechanisms underlying the two conditions.     

Auditory adaptation in voice perception

Perceptual aftereffects following adaptation to simple stimulus attributes (e.g., motion, color) have been studied for hundreds of years. A striking recent discovery was that adaptation also elicits contrastive aftereffects in visual perception of complex stimuli and faces [1-6]. Here, we show for the first time that adaptation to nonlinguistic information in voices elicits systematic auditory aftereffects. Prior adaptation to male voices causes a voice to be perceived as more female (and vice versa), and these auditory aftereffects were measurable even minutes after adaptation. By contrast, crossmodal adaptation effects were absent, both when male or female first names and when silently articulating male or female faces were used as adaptors. When sinusoidal tones (with frequencies matched to male and female voice fundamental frequencies) were used as adaptors, no aftereffects on voice perception were observed. This excludes explanations for the voice aftereffect in terms of both pitch adaptation and postperceptual adaptation to gender concepts and suggests that contrastive voice-coding mechanisms may routinely influence voice perception. The role of adaptation in calibrating properties of high-level voice representations indicates that adaptation is not confined to vision but is a ubiquitous mechanism in the perception of nonlinguistic social information from both faces and voices.     

Perception of the consequences of self-action is temporally tuned and event driven

It has been proposed that in order to increase the salience of sensations with an external cause, sensations that are predictable based on one's own actions are attenuated [1 and 2]. This may explain why self-imposed tickle [3 and 4] or constant forces [5] are perceived as less intense than the same stimuli externally imposed. Here, subjects used their right index finger to tap a force sensor mounted above their left index finger. When a motor generated a tap on the left finger synchronously with the right tap, simulating contact between the fingers, the perception of force in the left finger was attenuated compared to the same tap experienced during rest. Attenuation gradually reduced as the left tap was either delayed or advanced relative to the active right tap. However, no attenuation was seen to left taps triggered by right-finger movements that stopped above or passed wide of the sensor. We conclude that there is a window of sensory attenuation that is broadly temporally tuned and centered on the time at which the fingers would normally make contact. That is, predictive tactile sensory attenuation is linked to specific external events arising from movement rather than to the movement per se.     

Perceived Loudness of Self-Generated Sounds Is Differentially Modified by Expected Sound Intensity

Performing actions with sensory consequences modifies physiological and behavioral responses relative to otherwise identical sensory input perceived in a passive manner. It is assumed that such modifications occur through an efference copy sent from motor cortex to sensory regions during performance of voluntary actions. In the auditory domain most behavioral studies report attenuated perceived loudness of self-generated auditory action-consequences. However, several recent behavioral and physiological studies report enhanced responses to such consequences. Here we manipulated the intensity of self-generated and externally-generated sounds and examined the type of perceptual modification (enhancement vs. attenuation) reported by healthy human subjects. We found that when the intensity of self-generated sounds was low, perceived loudness is enhanced. Conversely, when the intensity of self-generated sounds was high, perceived loudness is attenuated. These results might reconcile some of the apparent discrepancies in the reported literature and suggest that efference copies can adapt perception according to the differential sensory context of voluntary actions.     

Giving the Giggles: Prediction, Intervention, and Young Children's Representation of Psychological Events

Adults recognize that if event A predicts event B, intervening on A might generate B. Research suggests that young children have difficulty making this inference unless the events are initiated by goal-directed actions [1]. The current study tested the domain-generality and development of this phenomenon. Replicating previous work, when the events involved a physical outcome, toddlers (mean: 24 months) failed to generalize the outcome of spontaneously occurring predictive events to their own interventions; toddlers did generalize from prediction to intervention when the events involved a psychological outcome. We discuss these findings as they bear on the development of causal concepts.     

精神分裂症视觉周边抑制异常及其神经机制

精神分裂症患者普遍存在视觉信息处理异常,这些视知觉功能紊乱涉及视通路的高级以及低级视区,表明在部分精神分裂症患者中,视觉系统早期或晚期的不同信息处理阶段均可能存在损伤.阐明这些感知觉信息处理紊乱的神经机制对理解精神分裂症神经病理生理学机制有重大意义.视觉周边抑制(surround suppression)是一种广泛存在的视觉现象,指在神经生理水平或视知觉水平上外周对中央视觉目标的抑制作用.精神分裂症的视觉周边抑制发生异常改变,然而其损伤状况并不完全一致,且其具体神经机制目前仍不清楚.本文以周边抑制为对象,从精神分裂症周边抑制改变状况及其神经机制两个层面简述了国内外精神分裂症视觉周边抑制的研究进展.未来研究方向需要系统全面地调查精神分裂症周边抑制损伤状况,综合脑科学研究技术共同探究精神分裂症患者周边抑制异常的具体神经环路.     

Learning to use an invisible visual signal for perception

How does the brain construct a percept from sensory signals? One approach to this fundamental question is to investigate perceptual learning as induced by exposure to statistical regularities in sensory signals [1-7]. Recent studies showed that exposure to novel correlations between sensory signals can cause a signal to have new perceptual effects [2, 3]. In those studies, however, the signals were clearly visible. The automaticity of the learning was therefore difficult to determine. Here we investigate whether learning of this sort, which causes new effects on appearance, can be low level and automatic by employing a visual signal whose perceptual consequences were made invisible-a vertical disparity gradient masked by other depth cues. This approach excluded high-level influences such as attention or consciousness. Our stimulus for probing perceptual appearance was a rotating cylinder. During exposure, we introduced a new contingency between the invisible signal and the rotation direction of the cylinder. When subsequently presenting an ambiguously rotating version of the cylinder, we found that the invisible signal influenced the perceived rotation direction. This demonstrates that perception can rapidly undergo "structure learning" by automatically picking up novel contingencies between sensory signals, thus automatically recruiting signals for novel uses during the construction of a percept.