Pre-cue fronto-occipital alpha phase and distributed cortical oscillations predict failures of cognitive control

Cognitive control is required for correct performance on antisaccade tasks, including the ability to inhibit an externally driven ocular motor response (a saccade to a peripheral stimulus) in favor of an internally driven ocular motor goal (a saccade directed away from a peripheral stimulus). Healthy humans occasionally produce errors during antisaccade tasks, but the mechanisms associated with such failures of cognitive control are uncertain. Most research on cognitive control failures focuses on poststimulus processing, although a growing body of literature highlights a role of intrinsic brain activity in perceptual and cognitive performance. The current investigation used dense array electroencephalography and distributed source analyses to examine brain oscillations across a wide frequency bandwidth in the period before antisaccade cue onset. Results highlight four important aspects of ongoing and preparatory brain activations that differentiate error from correct antisaccade trials: (1) ongoing oscillatory beta (20-30 Hz) power in anterior cingulate before trial initiation (lower for error trials); (2) instantaneous phase of ongoing alpha/theta (7 Hz) in frontal and occipital cortices immediately before trial initiation (opposite between trial types); (3) gamma power (35-60 Hz) in posterior parietal cortex 100 ms before cue onset (greater for error trials); and (4) phase locking of alpha (5-12 Hz) in parietal and occipital cortices immediately before cue onset (lower for error trials). These findings extend recently reported effects of pre-trial alpha phase on perception to cognitive control processes and help identify the cortical generators of such phase effects.     

Auditory gamma oscillations predict global symptomatic outcome in the early stages of psychosis: A longitudinal investigation

Objectives

The gamma-band auditory steady-state response (ASSR) is thought to reflect the function of parvalbumin-positive γ-aminobutyric acid (GABA)-ergic interneurons and may be a candidate biomarker in early psychosis. Although previous cross-sectional studies have shown that gamma-band ASSR is reduced in early psychosis, whether reduced gamma-band ASSR could be a predictor of the long-term prognosis remains unknown.

Neuronal communication within synchronous gamma oscillations

The gamma-band oscillatory activity notably appears in the primary sensory and motor cortical areas. Because both sensory and motor responses are characterized by many static and dynamic variables, questions are raised regarding how cortical neurons manage to transmit analog information within the gammaoscillatory activity. Here, a possible way of communication among pyramidal neurons in the gamma frequency range is proposed based on the sampling theorem in communication theory.     

Lewy body densities in the entorhinal and anterior cingulate cortex predict cognitive deficits in Parkinson's disease

Previous studies reported an association between cortical Lewy body (LB) formation and dementia in Parkinson's disease (PD). However, it is unclear whether cognitive decline in this disorder is related to specific patterns of LB distribution within the cerebral cortex. Moreover, the prediction of cognitive status based on concomitant assessment of LB and Alzheimer's disease lesions has led to conflicting results. We performed a clinicopathological study in 22 elderly PD patients in whom parkinsonism preceded cognitive decline by at least 3 years. Cognitive status was assessed prospectively using the clinical dementia rating scale (CDR); quantitative assessment of LB, neurofibrillary tangles (NFT), and senile plaques (SP) was performed in Brodmann areas 9, 21, 24, 40 and the entorhinal cortex. Statistical analysis was performed using both correlation coefficients and logistic regression models. There was a highly significant correlation between CDR scores and regional LB scores in the entorhinal cortex and area 24. LB and SP densities in the entorhinal cortex accounted for 36.2% and 19.3% of the variability in CDR scores. LB densities in area 24 could explain 25.2% of this variability. NFT densities did not predict cognitive status. In multivariate models only LB densities in the entorhinal cortex and anterior cingulate cortex were significantly associated with CDR scores. These results imply that an assessment of LB pathology limited to the entorhinal cortex and area 24 may be sufficient to predict cognition in PD. They also suggest that LB formation in limbic areas may be crucial for the development of PD dementia.     

Hearing and seeing meaning in noise: Alpha,beta, and gamma oscillations predict gestural enhancement of degraded speech comprehension

During face‐to‐face communication, listeners integrate speech with gestures. The semantic information conveyed by iconic gestures (e.g., a drinking gesture) can aid speech comprehension in adverse listening conditions. In this magnetoencephalography (MEG) study, we investigated the spatiotemporal neural oscillatory activity associated with gestural enhancement of degraded speech comprehension. Participants watched videos of an actress uttering clear or degraded speech, accompanied by a gesture or not and completed a cued‐recall task after watching every video. When gestures semantically disambiguated degraded speech comprehension, an alpha and beta power suppression and a gamma power increase revealed engagement and active processing in the hand‐area of the motor cortex, the extended language network (LIFG/pSTS/STG/MTG), medial temporal lobe, and occipital regions. These observed low‐ and high‐frequency oscillatory modulations in these areas support general unification, integration and lexical access processes during online language comprehension, and simulation of and increased visual attention to manual gestures over time. All individual oscillatory power modulations associated with gestural enhancement of degraded speech comprehension predicted a listener's correct disambiguation of the degraded verb after watching the videos. Our results thus go beyond the previously proposed role of oscillatory dynamics in unimodal degraded speech comprehension and provide first evidence for the role of low‐ and high‐frequency oscillations in predicting the integration of auditory and visual information at a semantic level.     

Human EEG gamma oscillations in neuropsychiatric disorders

Due to their small amplitude, the importance of high-frequency EEG oscillations with respect to cognitive functions and disorders is often underestimated as compared to slower oscillations. This article reviews the literature on the alterations of gamma oscillations (about 30-80 Hz) during the course of neuropsychiatric disorders and relates them to a model for the functional role of these oscillations for memory matching. The synchronous firing of neurons in the gamma-band has been proposed to bind multiple features of an object, which are coded in a distributed manner in the brain, and is modulated by cognitive processes such as attention and memory. In certain neuropsychiatric disorders the gamma activity shows significant changes. In schizophrenic patients, negative symptoms correlate with a decrease of gamma responses, whereas a significant increase in gamma amplitudes is observed during positive symptoms such as hallucinations. A reduction is also observed in Alzheimer's Disease (AD), whereas an increase is found in epileptic patients, probably reflecting both cortical excitation and perceptual distortions such as déjà vu phenomena frequently observed in epilepsy. ADHD patients also exhibit increased gamma amplitudes. A hypothesis of a gamma axis of these disorders mainly based on the significance of gamma oscillations for memory matching is formulated.     

Beta oscillations reflect memory and motor aspects of spoken word production

Two major components form the basis of spoken word production: the access of conceptual and lexical/phonological information in long‐term memory, and motor preparation and execution of an articulatory program. Whereas the motor aspects of word production have been well characterized as reflected in alpha‐beta desynchronization, the memory aspects have remained poorly understood. Using magnetoencephalography, we investigated the neurophysiological signature of not only motor but also memory aspects of spoken‐word production. Participants named or judged pictures after reading sentences. To probe the involvement of the memory component, we manipulated sentence context. Sentence contexts were either constraining or nonconstraining toward the final word, presented as a picture. In the judgment task, participants indicated with a left‐hand button press whether the picture was expected given the sentence. In the naming task, they named the picture. Naming and judgment were faster with constraining than nonconstraining contexts. Alpha‐beta desynchronization was found for constraining relative to nonconstraining contexts pre‐picture presentation. For the judgment task, beta desynchronization was observed in left posterior brain areas associated with conceptual processing and in right motor cortex. For the naming task, in addition to the same left posterior brain areas, beta desynchronization was found in left anterior and posterior temporal cortex (associated with memory aspects), left inferior frontal cortex, and bilateral ventral premotor cortex (associated with motor aspects). These results suggest that memory and motor components of spoken word production are reflected in overlapping brain oscillations in the beta band. Hum Brain Mapp 36:2767–2780, 2015. © 2015 Wiley Periodicals, Inc.     

Symptomatological and cognitive predictors of insight in chronic schizophrenia

Studies of schizophrenia show lack of agreement about the relationship of symptomatological and cognitive factors to insight. In this study, positive and negative symptomatology and cognitive function were assessed by the Positive and Negative Syndrome Scale (PANSS), the Wisconsin Card Sorting Test (WCST), and the Wechsler Adult Intelligence Scale Revised (WAIS-R) in male chronic schizophrenic patients in relation to level of insight measured with the Japanese version of the Schedule for the Assessment of Insight (SAI-J). Negative symptoms were significantly and negatively associated with overall insight, particularly with treatment compliance and recognition of mental illness. The present findings suggest that aspects of insight such as treatment compliance and recognition of mental illness are negatively associated with negative symptoms.     

The relationship between cognitive insight, clinical insight, and depression in patients with schizophrenia

Despite comorbid depression being relatively common even in subjects with schizophrenia, to the best of our knowledge, there is, to date, no report in the literature specifically and detailed examining the cognitive and clinical insight in subjects with schizophrenia and a comorbid depressive syndrome. Hence, in this study, we sought to compare the cognitive and clinical insight in our subjects with schizophrenia with and without a comorbid depressive syndrome. We found that participants in the depressive group scored significantly higher on self-reflectiveness and the reflectiveness-certainty (R-C) index scores than those in the nondepressive group. There was no significant difference among groups on the Scale for the Assessment of Positive Symptoms, Scale for the Assessment of Negative Symptoms, and clinical insight scores assessed by the Scale to Assess Unawareness of Mental Disorder. In addition, self-reflectiveness scores significantly correlated with depression, observed depression, hopelessness, and suicidality subscores of the Calgary Depression Scale for Schizophrenia. A better understanding of the cognitive component of insight in schizophrenia with comorbid depression may contribute to develop more efficient cognitive strategies, thus improving patient outcome. However, clinicians should be aware of the possibility of exacerbating a sense of hopelessness and suicide risk during the interventions that improve cognitive insight.     

Evidence that health attributions and symptom severity predict insight in schizophrenia

Although a relationship between insight and symptomatology in schizophrenia has been repeatedly demonstrated, the influence of psychological variables such as coping mechanisms and attributional style is less clear. We evaluated health attributions, subjective resources for coping, symptomatology, general cognitive functioning, and insight among 38 consecutive admissions with DSM-III-R schizophrenia from a geographically defined catchment area. Health attributions accounted for a significant amount of insight even after symptom severity was accounted for and together predicted 32% of variation in insight scores. This study emphasizes the multifactorial nature of insight and the importance of psychological variables in addition to symptomatology.     

High‐frequency gamma oscillations coexist with low‐frequency gamma oscillations in the rat visual cortex in vitro

Synchronization of neuronal activity in the visual cortex at low (30–70 Hz) and high gamma band frequencies (> 70 Hz) has been associated with distinct visual processes, but mechanisms underlying high‐frequency gamma oscillations remain unknown. In rat visual cortex slices, kainate and carbachol induce high‐frequency gamma oscillations (fast‐γ; peak frequency ～ 80 Hz at 37°C) that can coexist with low‐frequency gamma oscillations (slow‐γ; peak frequency ～ 50 Hz at 37°C) in the same column. Current‐source density analysis showed that fast‐γ was associated with rhythmic current sink‐source sequences in layer III and slow‐γ with rhythmic current sink‐source sequences in layer V. Fast‐γ and slow‐γ were not phase‐locked. Slow‐γ power fluctuations were unrelated to fast‐γ power fluctuations, but were modulated by the phase of theta (3–8 Hz) oscillations generated in the deep layers. Fast‐γ was spatially less coherent than slow‐γ. Fast‐γ and slow‐γ were dependent on γ‐aminobutyric acid (GABA)_A receptors, α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors and gap‐junctions, their frequencies were reduced by thiopental and were weakly dependent on cycle amplitude. Fast‐γ and slow‐γ power were differentially modulated by thiopental and adenosine A₁ receptor blockade, and their frequencies were differentially modulated by N‐methyl‐d ‐aspartate (NMDA) receptors, GluK1 subunit‐containing receptors and persistent sodium currents. Our data indicate that fast‐γ and slow‐γ both depend on and are paced by recurrent inhibition, but have distinct pharmacological modulation profiles. The independent co‐existence of fast‐γ and slow‐γ allows parallel processing of distinct aspects of vision and visual perception. The visual cortex slice provides a novel in vitro model to study cortical high‐frequency gamma oscillations.     

Beta oscillations relate to the N400m during language comprehension

The relationship between the evoked responses (ERPs/ERFs) and the event‐related changes in EEG/MEG power that can be observed during sentence‐level language comprehension is as yet unclear. This study addresses a possible relationship between MEG power changes and the N400m component of the event‐related field. Whole‐head MEG was recorded while subjects listened to spoken sentences with incongruent (IC) or congruent (C) sentence endings. A clear N400m was observed over the left hemisphere, and was larger for the IC sentences than for the C sentences. A time–frequency analysis of power revealed a decrease in alpha and beta power over the left hemisphere in roughly the same time range as the N400m for the IC relative to the C condition. A linear regression analysis revealed a positive linear relationship between N400m and beta power for the IC condition, not for the C condition. No such linear relation was found between N400m and alpha power for either condition. The sources of the beta decrease were estimated in the LIFG, a region known to be involved in semantic unification operations. One source of the N400m was estimated in the left superior temporal region, which has been related to lexical retrieval. We interpret our data within a framework in which beta oscillations are inversely related to the engagement of task‐relevant brain networks. The source reconstructions of the beta power suppression and the N400m effect support the notion of a dynamic communication between the LIFG and the left superior temporal region during language comprehension. Hum Brain Mapp, 2012. © 2012 Wiley Periodicals, Inc.     

Developmental event-related gamma oscillations: effects of auditory attention

This study describes maturational changes in topographical patterns, stability, and functional reactivity of auditory gamma band (31-63 Hz) responses (GBRs) as brain electrical correlates relevant for cognitive development during childhood. GBRs of 114 healthy children from 9 to 16 years were elicited in an auditory focused attention task requiring motor responding to targets, and analyzed by means of the wavelet transform (WT). The effects of age and task variables (attended side and stimulus type relevance) were examined for GBR power and phase-locking within 120 ms after stimulation. Similar to the spontaneous gamma band power, the power and phase-synchronization of GBRs did not depend on the age. However, the functional reactivity of GBRs at specific locations changed in the course of development. In 9-12-year-old children, GBRs at frontal locations were larger and better synchronized to target than to nontarget stimulus type, and were larger over the left hemisphere (contralateral to the responding hand), thus manifesting sensitivity to external stimulus features and motor task. In 13-16-year-old adolescents, GBRs at parietal sites were enhanced by active attending to the side of stimulation, thus being associated with a maintenance of attentional focus to stimulus location. The results indicate that (i) specific aspects of task-stimulus processing engage distinct spatially localized gamma networks at functionally relevant areas, and (ii) the neuronal substrates of gamma band networks and the ability to synchronize them in relation to task-specific processes are available in all age groups from 9 to 16 years. However, the mode and efficiency with which gamma networks can be entrained depends on the age. This age-dependent reactivity of GBRs to different task variables may reflect a transition in processing strategies emerging at approximately 12-13 years in relation to the maturation of cognitive and executive brain functions.     

Running speed alters the frequency of hippocampal gamma oscillations

Successful spatial navigation is thought to employ a combination of at least two strategies: the following of landmark cues and path integration. Path integration requires that the brain use the speed and direction of movement in a meaningful way to continuously compute the position of the animal. Indeed, the running speed of rats modulates both the firing rate of neurons and the spectral properties of low frequency, theta oscillations seen in the local field potential (LFP) of the hippocampus, a region important for spatial memory formation. Higher frequency, gamma-band LFP oscillations are usually associated with decision-making, increased attention, and improved reaction times. Here, we show that increased running speed is accompanied by large, systematic increases in the frequency of hippocampal CA1 network oscillations spanning the entire gamma range (30-120 Hz) and beyond. These speed-dependent changes in frequency are seen on both linear tracks and two-dimensional platforms, and are thus independent of the behavioral task. Synchrony between anatomically distant CA1 regions also shifts to higher gamma frequencies as running speed increases. The changes in frequency are strongly correlated with changes in the firing rates of individual interneurons, consistent with models of gamma generation. Our results suggest that as a rat runs faster, there are faster gamma frequency transitions between sequential place cell-assemblies. This may help to preserve the spatial specificity of place cells and spatial memories at vastly different running speeds.     

Impaired cerebral glucose metabolism and cognitive functioning predict deterioration in mild cognitive impairment

The objective of this study was to assess whether reduced glucose metabolism (rCMRGlu) and cognitive functioning could predict development of Alzheimer's disease (AD) in subjects with mild cognitive impairment (MCI). Twenty MCI patients underwent baseline and follow-up investigations of rCMRGlu, as measured by PET, and cognitive function measured by neuropsychological test assessments. Subjects were clinically followed up with an average interval of 36.5 months. Two groups were obtained after the second clinical assessment. Nine patients were diagnosed as AD and classified as progressive MCI (P-MCI), whereas 11 patients remained clinically stable and were classified as stable MCI (S-MCI). There were no differences in demographic variables or baseline MMSE between the two subgroups. Logistic regression indicated the two variables that most effectively predicted future development of AD were rCMRGlu from the left temporoparietal area and performance on the block design. These combined measures gave an optimal 90% correct classification rate, whereas only rCMRGlu or neuropsychology alone gave 75% and 65% correct classification, respectively. Measures of temporoparietal cerebral metabolism and visuospatial function may aid in predicting the evolution to AD for patients with MCI.     

Human entorhinal gamma and theta oscillations selective for remote autobiographical memory

Current source densities in different layers of the human entorhinal cortex (ER) were recorded using a linear array of 24 microelectrodes during three memory conditions: a remote autobiographical condition eliciting recollections of events that occurred 10 or more years ago in the participant's past, a semantic icon condition invoking the mental image of a well‐known object, and a semantic knowledge condition asking about general information. Our data demonstrate theta, gamma, and delta oscillations in left ER particularly for remote autobiographical memory. Gamma is predominant in hippocampally projecting layers during presentation of the memory cue, whereas theta is prolonged and dominant in cortically projecting layers during memory retrieval. Gamma interactions between ER and hippocampal formation (HF) may elicit an HF contribution to recall under influences relayed from the association cortex (AC). This contribution may then be relayed back to AC during retrieval of the memory orchestrated by theta interactions with ER. Accordingly, theta oscillations were recorded simultaneously in frontal and temporal cortices. © 2009 Wiley‐Liss, Inc.     

Induced visual illusions and gamma oscillations in human primary visual cortex

Using magnetoencephalography, we studied the spatiotemporal properties of cortical responses in terms of event-related synchronization and event-related desynchronization to a range of stripe patterns in subjects with no neurological disorders. These stripes are known for their tendency to induce a range of abnormal sensations, such as illusions, nausea, dizziness, headache and attacks of pattern-sensitive epilepsy. The optimal stimulus must have specific physical properties, and maximum abnormalities occur at specific spatial frequency and contrast. Despite individual differences in the severity of discomfort experienced, psychophysical studies have shown that most observers experience some degree of visual anomaly on viewing such patterns. In a separate experiment, subjects reported the incidence of illusions and discomfort to each pattern. We found maximal cortical power in the gamma range (30-60 Hz) confined to the region of the primary visual cortex in response to patterns of 2-4 cycles per degree, peaking at 3 cycles per degree. This coincides with the peak of mean illusions and discomfort, also maximal for patterns of 2-4 cycles per degree. We show that gamma band activity in V1 is a narrow band function of spatial frequency. We hypothesize that the intrinsic properties of gamma oscillations may underlie visual discomfort and play a role in the onset of seizures.     

Dissociating self-reported cognitive complaint from clinical insight in schizophrenia

Whereas new pharmacological treatments are developed for cognitive impairments in schizophrenia, self-assessment of cognitive dysfunctioning besides their objective validity could be of interest in evaluating patients' motivation to engage in rehabilitation program. Nevertheless insight into symptoms is severely impaired in schizophrenia and is negatively linked with poor compliance. But it is yet unknown if patients with poor insight into their symptoms could have some insight into their cognitive impairments. The aim of this study was to explore the relationships existing between the cognitive complaint and the level of awareness of the disease in patients with schizophrenia. A total of 101 patients with DSM-IV schizophrenia or schizoaffective disorder and 60 control participants were recruited. Insight was assessed using the Scale to assess Unawareness of Mental Disorder (SUMD) and cognitive complaint intensity was assessed with the Scale to Investigate Cognition in Schizophrenia (SSTICS). Participants with schizophrenia displayed the same level of cognitive complaint when compared to healthy controls. Strong correlations were observed between SSTICS total score and duration of illness, levels of depression and state anxiety. Patients with a good insight into the therapeutic effects achieved with medication expressed a more important cognitive complaint. No correlations were found between the four others SUMD insight dimensions and total SSTICS score. The partial overlap of insight into illness and cognitive complaint suggests that insight is modular in schizophrenia. Assessment of cognitive complaint and awareness of illness need to be assessed before engagement in rehabilitation program.