Do schizophrenics not differentiate between perception and imagination? an EEG study using dimensional analysis

The algorithmic complexity of multichannel EEGs is sensitive to changes in behavior

Symbolic measures of complexity provide a quantitative characterization of the sequential structure of symbol sequences. Promising results from the application of these methods to the analysis of electroencephalographic (EEG) and event-related brain potential (ERP) activity have been reported. Symbolic measures used thus far have two limitations, however. First, because the value of complexity increases with the length of the message, it is difficult to compare signals of different epoch lengths. Second, these symbolic measures do not generalize easily to the multichannel case. We address these issues in studies in which both single and multichannel EEGs were analyzed using measures of signal complexity and algorithmic redundancy, the latter being defined as a sequence-sensitive generalization of Shannon's redundancy. Using a binary partition of EEG activity about the median, redundancy was shown to be insensitive to the size of the data set while being sensitive to changes in the subject's behavioral state (eyes open vs. eyes closed). The covariance complexity, calculated from the singular value spectrum of a multichannel signal, was also found to be sensitive to changes in behavioral state. Statistical separations between the eyes open and eyes closed conditions were found to decrease following removal of the 8- to 12-Hz content in the EEG, but still remained statistically significant. Use of symbolic measures in multivariate signal classification is described.

Both pain and EEG response to cold pressor stimulation occurs faster in fibromyalgia patients than in control subjects

Pain-evoked brain potentials elicited by laser stimulation have been repeatedly shown to be abnormal in fibromyalgia syndrome. However, to our knowledge this is the first study assessing enduring (cold pressor) pain and correlated EEG changes in fibromyalgia. EEG power and subjective pain ratings during the cold pressor test were analyzed and contrasted with tasks not involving sensory stimulation (rest, mental arithmetic and pain imagery) in 20 patients with fibromyalgia and 21 healthy control subjects. Fibromyalgia patients both perceived pain and judged pain as intolerable earlier than control subjects, while pain intensity ratings and EEG power changes during subjective awareness of pain were similar in both groups. In patients and control subjects, pain was correlated with a rise in delta, theta and beta power. EEG power spectra during pain imagery and mental arithmetic were significantly different from those observed during the cold pressor test. In conclusion, fibromyalgia patients seem to process painful stimuli abnormally in a quantitative sense, thus producing both the sensation of pain, as well as the associated EEG patterns, much earlier than control subjects. However, the quality of the pain-associated EEG changes seems similar.

First-episode schizophrenics show normal duration and topography of quasistationary EEG segments as compared to controls, during rest as well as during active tasks

In patients suffering from chronic schizophrenia, both altered temporospatial structure of the EEG and impaired activation during cognitive tasks have repeatedly been demonstrated. The present study evaluates whether similar abnormalities are present in drug-naive first-episode schizophrenics. The EEGs of 32 schizophrenic patients and of 52 healthy controls were recorded during a simple and a complicated motor task, a simple and a complicated auditory stimulus, and during resting periods between the tasks. The temporospatial characteristics were evaluated by adaptive segmentation of EEG, which decomposes an EEG into temporal segments of quasistationary activity. No differences in the temporal and topographic aspects of the EEGs were found between the first-episode schizophrenic patients and the controls, neither during the resting EEGs nor during active tasks. Moreover, the dynamic course of the EEGs, defined as the alternation between task-related changes of temporospatial patterns and the reappearance of resting patterns, was identical in patients and controls. The present findings suggest that while abnormal EEG power spectra seem a consistent finding in treated as well as in never-treated schizophrenics, altered temporospatial patterns and reduced task-related EEG changes are inconsistent signs.

Redox mechanisms at the glutamate synapse and their significance: a review

This paper reviews what is currently known about the redox state of the glutamate synapse and its possible role in modulating synaptic plasticity and thus learning and neurocomputation. The hypothesis is presented that the growth or pruning of the synaptic spine is controlled in part by the balance in the synapse between neurodestructive pro-oxidants (e.g., nitric acid radical and hydrogen peroxide) and neuroprotective antioxidants (e.g., ascorbate and carnosine). In addition, there may be a role for catecholamines, in particular dopamine, related to its role in reinforcement signalling. Activation of the dopamine D2 receptor induces the synthesis of an antioxidant enzyme, possibly catalase. Dopamine may also affect the redox balance in the glutamate synapse directly by diffusion from the adjacent dopaminergic bouton-en-passage. Catecholamines are powerful antioxidants, scavengers of free radicals and iron chelators. Catecholamine-iron complexes are potent dismuters of superoxide ions. Additional agents participating in spine pruning may be neurotoxic catecholamine o-quinones present in the brain. This system may be at fault in schizophrenia and Parkinson's disease. Experiments to test the hypothesis are suggested.

Decreased duration and altered topography of electroencephalographic microstates in patients with panic disorder

The topography and temporal sequence of scalp electrical fields were analyzed by adaptive segmentation of the continuous electroencephalogram (EEG) in 27 patients with panic disorder and 28 control subjects during rest phases and during the viewing of a neutral (mushroom) or an emotionally relevant (casualty) picture. The results indicate decreased duration of brain microstates in panic patients during all conditions. Comparison of the resting phases with the viewing conditions revealed a significant acceleration of EEG microstates in both the patients and the control subjects. Patients and control subjects differed in the topography of the fields during rest: control subjects showed a left-anterior/right-posterior orientation, while panic patients showed a predominantly right-anterior/left-posterior orientation. Neither group displayed any topographic changes when viewing the mushroom picture. However, when viewing the anxiety-specific casualty picture, panic patients shifted fields in a different way than did control subjects. Centroid topography does not permit clear localization of the cortical generators. It is concluded that panic patients show a generally increased cortical activation compared with healthy control subjects, and activate different neuronal arrays when viewing an anxiety-specific stimulus.

Global, regional, and local measures of complexity of multichannel electroencephalography in acute, neuroleptic-naive, first-break schizophrenics

BACKGROUND

Schizophrenic symptoms commonly are felt to indicate a loosened coordination, i.e. a decreased connectivity of brain processes.

METHODS

To address this hypothesis directly, global and regional multichannel electroencephalographic (EEG) complexities (omega complexity and dimensional complexity) and single channel EEG dimensional complexities were calculated from 19-channel EEG data from 9 neuroleptic-naive, first-break, acute schizophrenics and 9 age- and sex-matched controls. Twenty artifact-free 2 second EEG epochs during resting with closed eyes were analyzed (2-30 Hz bandpass, average reference for global and regional complexities, local EEG gradient time series for single channels).

RESULTS

Anterior regional Omega-Complexity was significantly increased in schizophrenics compared with controls (p < 0.001) and anterior regional Dimensional Complexity showed a trend for increase. Single channel Dimensional Complexity of local gradient waveshapes was prominently increased in the schizophrenics at the right precentral location (p = 0.003).

CONCLUSIONS

The results indicate a loosened cooperativity or coordination (vice versa: an increased independence) of the active brain processes in the anterior brain regions of the schizophrenics.

Dynamical aspects of the EEG in different psychopathological states in an interview situation: a pilot study

Dynamical brain states can be characterized by non-linear measures of EEG. The present study shows that critical transitions, i.e., abrupt changes from one dynamic pattern of neural mass activity to another one, may be detected by abrupt variations in local chaoticity. Using an ambulatory device, EEG was recorded from 10 patients with a schizophrenic and two patients with an affective disorder during a series of 25-min interviews. Dynamical aspects, in particular, phase transitions in the EEG-dynamics of the EEG were characterized by means of a measure that continuously estimates the chaoticity of the EEG signal and is thus related to its predictability. Results indicate simpler dynamics of the EEG time series in paranoid-hallucinatory patients, while at the same time these patients tended to exhibit more abrupt transitions/unit of time between different dynamical EEG states. Such sudden phase transitions in brain activity were significantly enhanced prior to expressions of thought disorders that were detected by the interviewer and an observer in the conversation, compared with time periods during the interview without such symptoms.

Adrenocorticotropin widens the focus of attention in humans. A nonliner electroencephalographic analysis

OBJECTIVE

This study examined the effects of ACTH 4-10, a fragment of adrenocorticotropin (ACTH) with known central nervous system (CNS) activity, on the dimensional complexity of the ongoing electroencephalographic (EEG) activity. Stressful stimuli cause ACTH to be released from the pituitary, and as a neuropeptide ACTH may concurrently exert adaptive influences on the brain's processing of these stimuli. Previous studies have indicated an impairing influence of ACTH on selective attention.

METHODS

Dimensional complexity of the EEG, which indexes the brain's way of stimulus processing, was evaluated while subjects performed tasks with different attention demands. Sixteen healthy men (23 to 33 years) were tested once after placebo and another time after administration of ACTH 4-10 (1.25 mg intravenously (i.v.), 30 minutes before testing). The EEG was recorded while subjects were presented with a dichotic listening task (consisting of the concurrent presentation of tone pips to the left and right ear). Subjects either a) listened to pips in both ears (divided attention), or b) listened selectively to pips in one ear (selective attention), or c) ignored all pips.

RESULTS

Dimensional complexity of the EEG was higher during divided than selective attention. ACTH significantly increased the EEG complexity during selective attention, in particular over the midfrontal cortex (Fz, Cz).

CONCLUSIONS

The effects support the view of a de-focusing action of ACTH during selective attention that could serve to improve the organism's adaptation to stress stimuli.

Regulation of human thought by neuropeptide ACTH 4-10: an analysis of the EEG's dimensional complexity

The neuroactive 4-10 fragment of adrenocorticotropin (ACTH 4-10) has been found to impair electroencephalographic (EEG) signs of selective attention in previous studies. It was hypothesized that this effect reflects a more general influence of the peptide weakening the mutual inhibition among frontocortical neuronal networks. Therefore, ACTH 4-10 was expected to loosen attentional control not only over external input but also over internal thoughts. This study examined the effects of ACTH 4-10 on the dimensional complexity of the EEG recorded while subjects solved tasks of convergent analytical thinking and of divergent creative thinking and during mental relaxation. Subjects were tested 30 min after i.v. administration of placebo or ACTH 4-10 (2 mg). ACTH 4-10 enhanced dimensional complexity of the EEG. The effect primarily concerned frontocortical recordings during convergent thinking, which, following placebo, was associated with the lowest EEG dimension. ACTH 4-10 also impaired behavioral performance on tasks of convergent thought, when presented verbally. Results suggest that ACTH 4-10 counteracts the inhibitory control among cortical neuronal networks necessary for orderly analytical thinking.

Non-linear analysis of emotion EEG: calculation of Kolmogorov entropy and the principal Lyapunov exponent

For 76 healthy subjects, two non-linear measures, capturing the dynamical properties of the system orbiting within the attractor (i.e. Kolmogorov entropy, K2 and principal Lyapunov exponent, L1), were calculated from EEG segments, corresponding to different states of brain activity, induced by emotionally valenced (i.e. neutral, affective positive and negative) video stimuli. Significantly elevated values of EEG K2 and L1 in response to both positive and negative film categories as compared to neutral one were evidenced. Relying on the obtained findings, it is suggested that increased cortical dynamics, up to a certain level, are probably necessary for emotion functioning.