Supplements to Clinical neurophysiology最新文献

This report presents six cardinal results obtained with methods of oscillatory brain dynamics in euthymic and manic bipolar patients in comparison to healthy controls. Measurements include changes in oscillatory response activities in the theta, alpha, beta, and gamma frequency ranges. The analysis shows that spontaneous and response activities in the alpha range are highly reduced in euthymic and manic patients, respectively; conversely, beta responses are increased in euthymic and manic patients. Lithium use seems to be associated with further and significant increase in the beta frequency range in euthymic patients. Theta responses to auditory target stimulus during odd-ball paradigm appeared in two different frequency bands (4-6 and 6-8 Hz) in healthy participants. However, only fast theta responses were highly reduced under cognitive load in drug-free euthymic patients. The analysis of connectivity was performed by assessment of long-distance coherence function in the gamma frequency range. Both manic and euthymic patients presented significantly decreased fronto-temporal coherence function during visual odd-ball task, indicating a selective reduction in connectivity during cognitive processing. The present report also discusses that these six oscillatory parameters may serve as an ensemble of biomarkers for diagnostic purposes and tracking treatment response in bipolar disorder.

Animal models and endophenotypes of mental disorders are regarded as preclinical heuristic approaches aiming at understanding the etiopathogenesis of these diseases, and at developing drug treatment strategies. A frequently used translational model of sensorimotor gating and its deficits in some neuropsychiatric disorders is prepulse inhibition (PPI) of startle. PPI is reduced in schizophrenia patients, but the exact relationship between symptoms and reduced PPI is still unclear. Recent findings suggest that the levels of PPI in humans and animals may be predictive of certain cognitive functions. Hence, this simple measure of reflex suppression may be of use for clinical research. PPI is the reduction of the acoustic startle response that occurs when a weak prestimulus is presented shortly prior to a startling noise pulse. It is considered a measure of sensorimotor gating and is regulated by a cortico-limbic striato-pallidal circuit. However, PPI does not only occur in the domain of startle. PPI of alpha, gamma, and theta oscillations at frontal and central locations has been found, suggesting a relationship between PPI and cognitive processes. In fact, levels of PPI in healthy subjects and in animals predict their performance in cognitive tasks mainly mediated by the frontal cortex. Taken together, PPI might reflect a more general filtering performance leading to gating of intrusive sensory, motor, and cognitive input, thereby improving cognitive function. Hence, PPI might be used in clinical settings to predict the impact of drugs or psychotherapy on cognitive performance in neuropsychiatric patients.

Electrophysiological methods have demonstrated disturbances of neural synchrony and oscillations in schizophrenia which affect a broad range of sensory and cognitive processes. These disturbances may account for a loss of neural integration and effective connectivity in the disorder. The mechanisms responsible for alterations in synchrony are not well delineated, but may reflect disturbed interactions within GABAergic and glutamatergic circuits, particularly in the gamma range. Auditory steady-state responses (ASSRs) provide a non-invasive technique used to assess neural synchrony in schizophrenia and in animal models at specific response frequencies. ASSRs are electrophysiological responses entrained to the frequency and phase of a periodic auditory stimulus generated by auditory pathway and auditory cortex activity. Patients with schizophrenia show reduced ASSR power and phase locking to gamma range stimulation. We review alterations of ASSRs in schizophrenia, schizotypal personality disorder, and first-degree relatives of patients with schizophrenia. In vitro and in vivo approaches have been used to test cellular mechanisms for this pattern of findings. This translational, cross-species approach provides support for the role of N-methyl-D-aspartate and GABAergic dysregulation in the genesis of perturbed ASSRs in schizophrenia and persons at risk.

Background: Fronto-posterior networks have been implicated in cognitive control and understanding the detailed functional dynamics within this network is important to understand the pathophysiology of cognitive deficits in schizophrenia. In a previous study (Sharma et al., 2011), we found reduced event-related coherence between frontal and posterior electrode sites in delta and theta frequencies during cognitive control in schizophrenia. The current study aimed to look at the relationship between locally evoked frontal and posterior activity (measured by event-related potentials (ERPs)) and long-range coherence within the fronto-posterior network in healthy controls and patients with schizophrenia.

Methods: 16 schizophrenic/schizoaffective patients and 20 age-matched healthy controls performing a choice reaction task took part in the study. We examined ERPs occurring at frontal and posterior sites between 100 and 250 ms (overlapping with the time period where coherence deficits were previously found) for differences between patients and controls. ERPs examined were Pla/P2a and N1/N2b components occurring simultaneously during 100-200/200-250 ms post stimulus at the frontal (F5'/F6') and posterior (P7'/P8') sites, respectively. We further looked at group difference in event-related delta and theta fronto-posterior coherence in the exact same time windows as the ERPs and calculated the correlation between ERP amplitudes and simultaneous event-related delta and theta coherence for both hemispheres and time periods. Bonferroni correction was applied to correct for multiple correlations.

Results: We found a significant reduction in schizophrenia patients of the posterior N2b and a trend for reduction for the frontal P2a which are implicated in target-related information processing while the earlier frontal Pla and posterior N1 associated with more general sensory processing were relatively spared. However, the event-related coherence between the frontal and posterior areas was reduced in patients compared to controls during both the early and late time windows, indicating connectivity deficits to be a more consistent impairment in schizophrenia. There was limited linear correlation between fronto-posterior coherence and frontal and posterior ERP amplitudes but uncorrected correlation coefficients showed coherence in delta frequency to be correlated with P2a amplitude in both hemispheres and with Pla only in the left hemisphere in healthy controls. In the patients, however, this correlation was disrupted in the left hemisphere for both early and later stage evoked activity, whereas they showed a similar degree of correlation as healthy controls between P2a and delta coherence in the right hemisphere. Coherence in theta frequency showed no significant correlation with ERPs nor did N1/N2b show any significant correlation with coherence.

Conclusions: Impaired cognitiv

Current views of the genesis of the event-related potential (ERP) emphasize the contribution of ongoing oscillations - the ongoing electroencephalogram (EEG) is recognized as much more than "background noise" to be removed by response averaging to find the ERP. Early work from Başar's group noted that repetitive stimuli led to selective phase re-ordering of activity in the delta and alpha bands, such that enhanced brain negativity occurred at the time of the regular stimulus. Other work related negativity in alpha activity at stimulus onset to improved reaction times and ERP enhancements. These findings led us to begin a program of brain dynamics studies exploring pre-stimulus EEG phase states, their preferential occurrence in paradigms with regularly presented stimuli, and their relation to ERP outcomes. In particular, with very narrow EEG bands, we have repeatedly found that certain phase states preferentially occur at stimulus onset, implying ongoing phase re-ordering driven by stimulus occurrence. Effects are weakened with slightly varying inter-stimulus intervals, but still occur reliably. Further, these preferential phase states are functionally effective in relation to the ERP correlates of efficient stimulus processing. Preferential phase occurrence and their effects were originally reported in auditory oddball tasks, using narrow EEG bands derived by digital filtering. A recent study is presented illustrating generalization of the phenomenon in the auditory Go/NoGo task, using narrow bands derived by FFT techniques. Our current work is extending this research in normal children (to provide a comparative context for research in children with AD/HD), and well-functioning elderly (to provide a context for future work in relation to Alzheimer's disease).

Previous studies have found that event-related theta and gamma oscillations elicited in an auditory selective attention task are deviant in children with attention deficit/hyperactivity disorder (ADHD). It has been suggested that these deviations are associated with deficient motor inhibition in ADHD, which may lead to increased excitability of not only the motor generation networks but also the networks involved in sensory and cognitive processing of the stimulus requiring motor response. Within this suggestion, the present study used the same experimental database to compare the motor cortical activation of healthy controls and children with ADHD during the performance of the auditory selective attention task. Electroencephalography mu (8-12 Hz) activity at C3 and C4 electrodes was used as a measure of motor cortical activation. Mu power was analyzed for four stimulus conditions of the task (attended target, unattended target, attended nontarget, and unattended nontarget). It was found that motor cortical activation as reflected by mu power suppression was not overall greater in ADHD than healthy children. However, stimuli that possessed only partial target features and did not require motor responding (unattended target and attended nontarget) produced a significant reduction of mu activity in ADHD patients. These results suggest that motor cortical excitability is not generally increased in ADHD children. Rather, the co-existence of conflict features in complex stimuli induces task-irrelevant motor activation in these children. The deficient inhibition of motor cortical networks contralateral to the response may therefore be responsible for the functional asymmetry in stimulus processing in ADHD.

Method and concepts of brain oscillations pervade the neuroscience literature, especially in cognitive processes. Electrophysiological changes in patients with cognitive impairment will provide fundamental knowledge, not only for clinical studies but also, in turn, for understanding cognitive processes in healthy subjects. This review includes description of brain oscillations in schizophrenia, bipolar disorder, mild cognitive impairment, Alzheimer's disease, and attention deficit hyperactivity disorder. The reviewed publications include several methodological approaches: analysis of spontaneous electroencephalogram (EEG) spectra, evoked oscillations, event-related oscillations, and coherences both in spontaneous EEG and event-related oscillations. The review clearly shows that, in cognitive impairment, fundamental changes are observed in all diseases under study. Accordingly, oscillations can most probably be used as biomarkers in clinical studies. The conclusions of this review include several remarks indicating the nature of brain oscillations, their application to cognitive processes, and the usefulness of recording brain oscillations in memory loss, attention deficit, and learning.

The present article reviews findings from measuring evoked and event-related responses, neural oscillation and synchronization, and near-infrared spectroscopy (NIRS) studies in patients with bipolar disorder. Studies of evoked responses have indicated that the P50 suppression deficits may be related to the generation of psychosis and may constitute an endophenotype of bipolar disorder patients with psychotic features. The N100 may be intact in patients with bipolar disorder, and the N100 might be a biological index to distinguish bipolar disorder and schizophrenia. In studies of event-related responses, bipolar disorder patients appear to exhibit P300 abnormalities to some extent. In addition, some bipolar disorder patients may have preattentive dysfunction, indexed by abnormal mismatch negativities. Recent studies of neural oscillations suggest that bipolar disorder may be characterized by deficits in the auditory steady-state response. Moreover, bipolar patients may have altered gamma band responses, as well as abnormal beta and alpha activities perhaps related to deficits of fronto-temporal-parietal functional connectivity. NIRS studies of bipolar disorder have indicated hypofrontality during a verbal fluency task, and altered NIRS responses compared with those of patients with major depressive disorder or healthy subjects. In future studies, these techniques may be used to elucidate the neurophysiological abnormalities in patients with bipolar disorder. Moreover, neurophysiological approaches may reveal appropriate biological indices to distinguish bipolar disorder and schizophrenia, aiding the development of more effective medication at the early stages of illness.

The human brain contains an intricate network of about 100 billion neurons. Aging of the brain is characterized by a combination of synaptic pruning, loss of cortico-cortical connections, and neuronal apoptosis that provoke an age-dependent decline of cognitive functions. Neural/synaptic redundancy and plastic remodeling of brain networking, also secondary to mental and physical training, promote maintenance of brain activity and cognitive status in healthy elderly subjects for everyday life. However, age is the main risk factor for neurodegenerative disorders such as Alzheimer's disease (AD) that impact on cognition. Growing evidence supports the idea that AD targets specific and functionally connected neuronal networks and that oscillatory electromagnetic brain activity might be a hallmark of the disease. In this line, digital electroencephalography (EEG) allows noninvasive analysis of cortical neuronal synchronization, as revealed by resting state brain rhythms. This review provides an overview of the studies on resting state eyes-closed EEG rhythms recorded in amnesic mild cognitive impairment (MCI) and AD subjects. Several studies support the idea that spectral markers of these EEG rhythms, such as power density, spectral coherence, and other quantitative features, differ among normal elderly, MCI, and AD subjects, at least at group level. Regarding the classification of these subjects at individual level, the most previous studies showed a moderate accuracy (70-80%) in the classification of EEG markers relative to normal and AD subjects. In conclusion, resting state EEG makers are promising for large-scale, low-cost, fully noninvasive screening of elderly subjects at risk of AD.