Brain mechanisms involved in processing unreal perceptions

Visual Hallucinations and Impaired Conscious Visual Perception in Parkinson Disease

Visual hallucinations (VHs) are common in patients with Parkinson disease (PD), especially those with dementia, whereas auditory hallucinations are quite rare. Recent studies have revealed the involvement of several regions along the visual information-processing system that contribute to the pathophysiological mechanism of VHs: the eyes and retina, retinofugal projection, lateral geniculate nucleus, striate cortex, ventral pathways in the temporal cortices, and frontal and parietal cortices. In addition, the concurrent involvement of other systems in the brainstem and basal forebrain further modify VHs in PD. In this review, we discuss the pathophysiological association between the regional involvement of these areas and VHs.

Common coding and dynamic interactions between observed, imagined, and experienced motor and somatosensory activity

Motor imagery and perception - considered generally as forms of motor simulation - share overlapping neural representations with motor production. While much research has focused on the extent of this "common coding," less attention has been paid to how these overlapping representations interact. How do imagined, observed, or produced actions influence one another, and how do we maintain control over our perception and behavior? In the first part of this review we describe interactions between motor production and motor simulation, and explore apparent regulatory mechanisms that balance these processes. Next, we consider the somatosensory system. Numerous studies now support a "sensory mirror system" comprised of neural representations activated by either afferent sensation or vicarious sensation. In the second part of this review we summarize evidence for shared representations of sensation and sensory simulation (including imagery and observed sensation), and suggest that similar interactions and regulation of simulation occur in the somatosensory domain as in the motor domain. We suggest that both motor and somatosensory simulations are flexibly regulated to support simulations congruent with our sensorimotor experience and goals and suppress or separate the influence of those that are not. These regulatory mechanisms are frequently revealed by cases of brain injury but can also be employed to facilitate sensorimotor rehabilitation.

Distinct functional connectivity of limbic network in the washing type obsessive-compulsive disorder

Neurobiological models of obsessive-compulsive disorder (OCD) emphasize disturbances of the corticostriatal circuit, but it remains unclear as to how these complex network dysfunctions correspond to heterogeneous OCD phenotypes. We aimed to investigate corticostriatal functional connectivity alterations distinct to OCD characterized predominantly by contamination/washing symptoms. Functional connectivity strengths of the striatal seed regions with remaining brain regions during the resting condition and the contamination symptom provocation condition were compared among 13 OCD patients with predominant contamination/washing symptoms (CON), 13 OCD patients without these symptoms (NCON), and 18 healthy controls. The CON group showed distinctively altered functional connectivity between the ventral striatum and the insula during both the resting and symptom-provoking conditions. Also, the connectivity strength between the ventral striatum and the insula significantly correlated with contamination/washing symptom severity. As common connectivity alterations of the whole OCD subjects, corticostriatal circuits involving the orbitofrontal and temporal cortices were again confirmed. To our knowledge, this is the first study that examined specific abnormalities in functional connectivity of contamination/washing symptom dimension OCD. The findings suggest limbic network dysfunctions to play a pivotal role in contamination/washing symptoms, possibly associated with emotionally salient error awareness. Our study sample allowed us to evaluate the corticostriatal network dysfunction underlying the contamination/washing symptom dimension, which leaves other major symptom dimensions to be explored in the future.

Distinct neural responses used to gain insight into hallucinatory perception in patients with schizophrenia

OBJECTIVE

Most patients with schizophrenia suffer from various types of hallucinations, which commonly produce distress, functional disability or behavioral dyscontrol. The neural process of adapting to hallucinations in patients with schizophrenia remains unknown.

METHODS

Functional magnetic resonance imaging (MRI) responses to an unusual threatening visual stimulus designed to simulate a hallucinatory experience were compared between 16 patients with schizophrenia and 17 healthy controls. Linear and quadratic repetition-variant as well as repetition-invariant responses to the stimulus were compared between the two groups.

RESULTS

Repetition-invariant responses were similar between patients with schizophrenia and healthy controls. Patients with schizophrenia exhibited a linear activation pattern in the anterior cingulate, whereas healthy controls exhibited a parabolic activation pattern in the anterior prefrontal cortex, occipito-temporal junction and amygdala.

CONCLUSIONS

These results provide us with a better understanding of the neural processes involved in gaining insight into unreality. Patients with schizophrenia may use a salience-related region instead of reality monitoring-related regions to react to the unusual stimuli, and this peculiarity of the neural processes may be related to vulnerability to psychosis.

Dreaming and cognition in patients with frontotemporal dysfunction

Individuals with Parkinson's disease (PD) and temporal lobe epilepsy (TLE) have hallucinations and mild cognitive dysfunction. The objective of this work was to study dreams in PD and TLE patients using a common functional model of dream production involving the limbic and paralimbic structures. Dreams were characterised in early-stage PD (19 males) and TLE patients (52) with dream diaries classified by the Hall van de Castle system and were compared with matched controls. In PD, there were significant differences between patients' dreams and those of controls: animals, physical aggression, and a befriender were more common in patients, and aggressor and bodily misfortunes were less common. The dreams of patients with frontal dysfunction showed more aggressive features. TLE patients had lower recall than PD patients and a higher proportion of dreams involving family and familiar settings, lower proportions involving success, and a higher incidence of frontal dysfunction. The dreams of PD and TLE patients share important features.