Psychophysiological Investigations Research Articles

Comments for Current Interpretation EEG Alpha Activity: A Review and Analysis

Introduction: Exploring the EEG alpha oscillations generates considerable interest because there is well known its role in cognitive and psycho emotional aspects of human life. However, till now there isn’t well determined definition what is alpha activity phenomena and which indices are characterize it. Method: This article focuses on the attempt to determine EEG alpha-activity phenomena, its physical, molecular and morphological nature, to highlight its indices and their role in optimal functioning. Results: Specifically, this article examines individual alpha activity indices: 1) the individual alpha peak frequency; 2) activation magnitude measured by estimation the amount of alpha amplitude suppression in response to eyes open and individual alpha band width; 3) three alpha “autorhythmicity” indices: intra-spindle amplitude variability, spindle length and steepness. Conclusions: Throughout, the article provides a number of suggestions which alpha activity indices and in which conditions could be applied in psycho physiological investigations, what is their role in optimal functioning and what are possible directions for future research.

Symptoms of Anxiety and Depression Are Correlates of Angina Pectoris by Recent History and an Ischemia-Positive Treadmill Test in Patients with Documented Coronary Artery Disease in the Pimi Study

Objective. We tested the association of specific psychological characteristics in patients having stable coronary disease with the reporting of anginal symptoms during daily activities, and positive exercise testing. Methods. One hundred and ninety-six patients with documented CAD enrolled in the Psychophysiological Investigations of Myocardial Ischemia (PIMI) Study completed an anginal history questionnaire and a battery of psychometric tests. They also underwent standardized exercise treadmill tests. Results. Patients with a recent history of angina were more likely to be female, and had higher Beck Depression (P = .002), State Anxiety (P = .001), Trait Anxiety (P = .03), Harm Avoidance (P = .04) and Muscle Tension (P = .004) scores than patients who had no recent history of angina. Along with several treadmill variables indicating more severe disease state and reduced exercise tolerance, patients who developed angina on a positive treadmill test also displayed higher scores on the Beck Depression Inventory (P = .003) and State Anxiety (P = .004) scales. Conclusions. Several psychological characteristics, and most notably anxiety and depression, are strong correlates of recent angina and angina in the presence of ischemia provoked by treadmill testing.

Aesthetic images modulate emotional responses to reading news messages on a small screen: A psychophysiological investigation

Abstract pictures, such as artistic drawings, may evoke subtle emotions in their observers via aesthetic experiences. We examined among 44 participants the emotional responses as measured by facial electromyography (EMG) to aesthetic background images that varied on the emotional valence (unpleasant to pleasant) and arousal (calming to exciting) dimensions and were presented both separately and as background images for news messages. Effects of image arousal on free recall of news messages were also examined. A priori pleasant compared to unpleasant images were associated with higher orbicularis oculi EMG responses, both when presented alone and when presented as news message backgrounds. Analyses based on the participants' subjective pleasantness ratings also showed greater corrugator supercilii EMG activity for unpleasant compared to pleasant images. High-arousal as compared to low-arousal images improved recall for the superimposed news messages. In contrast, recall was not affected by a priori image valence or subjective pleasantness ratings. The results demonstrate that abstract images can be used to evoke emotional responses in the viewers that persist even when unrelated messages are superimposed on them. Similarly, high-arousal images can be used to enhance memory for superimposed textual messages.

A psychophysiological investigation of laterality in human emotion elicited by pleasant and unpleasant film clips

BackgroundResearch on laterality in emotion suggests a dichotomy between the brain hemispheres. The present study aimed to investigate this further using a modulated startle reflex paradigm.MethodsWe examined the effects of left and the right ear stimulation on the modulated startle reflex (as indexed by eyeblink magnitude, measured from the right eye) employing short (2 min) film clips to elicit emotions in 16 right-handed healthy participants. The experiment consisted of two consecutive sessions on a single occasion. The acoustic startle probes were presented monaurally to one of the ears in each session, counterbalanced across order, during the viewing of film clips.ResultsThe findings showed that eyeblink amplitude in relation to acoustic startle probes varied linearly, as expected, from pleasant through neutral to unpleasant film clips, but there was no interaction between monaural probe side and foreground valence.ConclusionsOur data indicate the involvement of both hemispheres when affective states, and associated startle modulations, are produced, using materials with both audio and visual properties. From a methodological viewpoint, the robustness of film clip material including audio properties might compensate for the insufficient information reaching the ipsilateral hemisphere when using static pictures. From a theoretical viewpoint, a right ear advantage for verbal processing may account for the failure to detect the expected hemispheric difference. The verbal component of the clips would have activated the left hemisphere, possibly resulting in an increased role for the left hemisphere in both positive and negative affect generation.

Perceived Recovery: A Psychophysiological investigation

PURPOSE: The aims of this study were to evaluate the ability of an individual to accurately perceive their own level of post-exercise recovery and to compare the pattern of perceived recovery with the recovery patterns of a number of potential mediating physiological parameters. METHODS: 17 well-trained males (means ± standard deviation for age, height, body mass, and body fat of the subjects were: 22 ± 4 years, 1.83 ± 0.05 m, 78.9 ± 7.6 kg, and 11.1 ± 2.2%, respectively) completed a series of 10 maximal sprint trials on an electromagnetically-braked cycle ergometer. Trial 1 evaluated peak power output from a maximal 5 s sprint. The remaining trials evaluated recovery after a 30 s sprint in the following ways: six of the trials evaluated the recovery of peak power using post-sprint stationary rest intervals of 5, 10, 20, 40, 80, and 160 s; two of the trials evaluated perceived recovery at those same time points via visual analogue scales; and the final trial evaluated physiological responses during five minutes of recovery. All trials were separated by a minimum of 48 hours and all data were normalised as a percentage of full recovery. RESULTS: The time point in recovery at which individuals perceived they had fully recovered was 163.3 ± 57.5 s. Power output at that same time point was 83.6 ± 5.2% of peak power. The results showed no significant differences between perceived recovery and the recovery processes of either VO2 (p = 0.06) or minute ventilation (VE) (p = 0.71). In contrast, there were significant differences (p < 0.05) between the time-courses of perceived recovery and those of core temperature, blood lactate, heart rate, respiratory rate, and respiratory exchange ratio. CONCLUSIONS: The results of this study show that the despite differences in the time-courses of perceived and actual recovery, individuals are able to closely predict full recovery time without the need for external timepieces. Moreover, the time-course of perceived recovery is similar to that of both VO2 and VE.

Non-Negative Multilinear Principal Component Analysis of Auditory Temporal Modulations for Music Genre Classification

Motivated by psychophysiological investigations on the human auditory system, a bio-inspired two-dimensional auditory representation of music signals is exploited, that captures the slow temporal modulations. Although each recording is represented by a second-order tensor (i.e., a matrix), a third-order tensor is needed to represent a music corpus. Non-negative multilinear principal component analysis (NMPCA) is proposed for the unsupervised dimensionality reduction of the third-order tensors. The NMPCA maximizes the total tensor scatter while preserving the non-negativity of auditory representations. An algorithm for NMPCA is derived by exploiting the structure of the Grassmann manifold. The NMPCA is compared against three multilinear subspace analysis techniques, namely the non-negative tensor factorization, the high-order singular value decomposition, and the multilinear principal component analysis as well as their linear counterparts, i.e., the non-negative matrix factorization, the singular value decomposition, and the principal components analysis in extracting features that are subsequently classified by either support vector machine or nearest neighbor classifiers. Three different sets of experiments conducted on the GTZAN and the ISMIR2004 Genre datasets demonstrate the superiority of NMPCA against the aforementioned subspace analysis techniques in extracting more discriminating features, especially when the training set has small cardinality. The best classification accuracies reported in the paper exceed those obtained by the state-of-the-art music genre classification algorithms applied to both datasets.

Psychophysiological correlates of different kinds of insight problems

Event Abstract Back to Event Psychophysiological correlates of different kinds of insight problems Alessandro Antonietti1, Barbara Colombo1*, Sandro DeSantis2 and Rosa A. Fabio2 1 Catholic University of Sacred Heart, Department of Psychology, Italy 2 University of Messina, Department of Psychology and Educational Sciences, Italy One of the main skills which education is aimed to enhance is problem-solving. Attempts to train problem-solving abilities should take into account the differences existing among different kinds of problems. Such differences can be supported by neurobiological measures. In this respect Jausovec and Bakracevic [1] reported different patterns of heart rate in step-by-step and insight problems. As far as insight problems are concerned, research has been based mostly on EEG and fMRI data [2, 3, 4] and no further psychophysiological investigation was carried out. Our goal was to refine the analysis of the psychophysiological counterparts of the solution process of insight problems. Thirty participants joined our research. After explaining the general procedure, a portable biofeedback was connected to the participant. The base line of psychophysiological activation was measured while participant was facing a relaxing visual presentation composed by landscaped photos. The biofeedback equipment was set in order to measure: skin conductance level, skin temperature, blood volume pulse, pulse volume amplitude, and pulse frequency. After recording the baseline, the experimental section started. Participants were faced with 16 problems which were designed to be not easily solved with incremental strategies, but required an insight. Problems were grouped into four categories (geometrical, instrumental, verbal, mathematical) according to the main strategy that should be use to reach the solution. Each problem was presented together with 4 possible solutions (1 right and 3 wrong). Participants had to tell aloud the letter associated with the right answer. After one minute another problem was presented. Data suggested that correct and incorrect solutions were preceded by different trends of hearth activity. Moreover, skin measures were influenced by the kind of problem: problems which were harder to solve induced increased level of concurrent activation.

Editorial: A Tribute to Yevgeniy Nikolaievich Sokolov (1920–2008)

On May 14, 2008, Professor Yevgeniy Nikolaievich Sokolov, of M.V. Lomonosov Moscow State University, passed away at age of 87. Professor Sokolov was born on September 23, 1920, in a family of civil servants residing in city of Nizhni Novgorod (Gorki). In 1939, he finished General Education with honors at School nr. 2 of Gorki. In 1940, he enrolled in Department of Naval Construction of Industrial Institute of same city. The German invasion of Soviet Union interrupted his studies, and he joined Soviet Army as a translator in Intelligence Units. Due to war merits, he was awarded Order of Red Star, Order of Great Patriotic War and medals For Victory over Germany in Great Patriotic War 1941-1945, For Defense of Moscow and For Liberation of Warsaw. Between 1945 and 1946, he studied at Maurice Thorez Pedagogical Institute of Moscow of Foreign Languages (specialty: modern German language), concluding his studies as an external student in only two years. In 1947, he carried out his doctorate studies in Psychology Section of Philosophy Institute of Academy of Sciences of USSR. This Psychology Section was directed by Sergey Leonidovich Rubinstein (1889-1960), who founded it in 1945 in Philosophy Institute, within framework of Psychological Laboratory of Professor Sergey Vasilievich Kravkov (1893-1951). There, Sokolov wrote his Candidature Thesis. The main topics that interested Kravkov (the interaction of sensory organs, nature of color vision, and electrophysiology of visual perception) had a notable influence on Sokolov's research interests. His Candidature Thesis, entitled Issues of Psychology of Perception from Pavlovian Approach was defended in 1950 and, besides analysis of Pavlovian heritage, it also included results of specific investigations of mechanisms of visual perception (subsequently, in 1958, these data were summarized in famous monograph Perception and Conditioned Reflex). Professor Kravkov, being a collaborator of Philosophy Institute, also carried out his investigations in Psychology Institute of Academy of Pedagogical Sciences of USSR, because in latter, in contrast to Philosophy Institute, there were proper conditions to perform real experiments. Sokolov also carried out many experiments there. In 1950, Sokolov was invited by Boris Mijailovich Teplov (1896-1965) to Moscow State University (MSU) to Psychology Department of Philosophy Faculty, directed by Teplov (S. L. Rubinstein had been dismissed and was only replaced in 1956 in Psychology Section of Philosophy Institute of Academy of Sciences of USSR). Between 1950-1960, Teplov's scientific work involved psychophysiology of individual differences, based on Pavlov's theory of properties of types of nervous system. Sokolov worked in Laboratory of Analyzers attached to Psychology Department of Philosophy Faculty. His first psychophysiological investigations in MSU were devoted to study of sensory processes involved in formation of mechanism of creation of elemental (primary) sensations of light and sound. Subsequently, these investigations were extended to include investigations of orientation reflex. Sokolov continued this work in collaboration with Physiology Department of Higher Nervous Activity of Biology Faculty of MSU. During these investigations, methods were developed to study structure of orienting reaction at different stages of appearance of conditioned reflex; an original model (which is still current nowadays) was proposed: the nervous model of stimulus, which explained dynamics of extinction (and recovery) of orienting reaction. In 1953, Alexandr Romanovich Luria (1902-1977) offered Sokolov a second post at his Laboratory in Institute of Defectology of Academy of Pedagogical Sciences of USSR, where objective recording methods of vegetative and electroencephalographic reactions were employed to diagnose vision and hearing alterations. …

Patterns of Objective Physical Functioning and Perception of Mood and Fatigue in Posttreatment Breast Cancer Patients and Healthy Controls: An Ambulatory Psychophysiological Investigation

To monitor objective physiological and self-report measures among apparently disease-free breast cancer patients (n = 33) in the first 2 years of posttreatment recovery, using a cross-sectional design, and compare findings with women without histories of cancer or other serious disorders (n =33). Time-since-treatment also served as an independent variable. Few studies have examined adjustment of breast cancer patients after primary treatment or objectively characterized posttreatment, everyday patterns of functioning. A 24-hour ambulatory minute-by-minute cardiorespiratory functioning and accelerometry activity were measured during one day, together with multiple repeated assessments of mood and fatigue. Traditional retrospective measures of well-being were also evaluated. Our ambulatory methodology permitted estimation of physiological rhythms of cardiorespiratory and accelerometry activity. Patients reported lower ambulatory levels of energy and poorer mood during the daytime than controls. Time-since-treatment was related directly to both momentary mood and energy as well as to objective measures of activity and respiratory parameters. Retrospective self-reports of impaired mood and symptoms persisted in patients, independently of time-since-treatment and of ambulatory physical or physiological activity. Ambulatory self-report data were associated with concurrent respiratory measures. Chemotherapy-related elevation of heart rate was found but was unrelated to self-report measures. Impaired sense of well being based on retrospective measures is not associated with pattern of physical or physiological functioning after treatment for breast cancer. However, ambulatory, momentary levels of mood and fatigue seem to be related to concurrent ventilatory activity and time-since-treatment. This is the first investigation that relates ambulatory and retrospective measures of affect and fatigue to concurrent, real-life physical functioning.

Depressive Symptoms Predict Heart Rate Recovery After Exercise Treadmill Testing in Patients With Coronary Artery Disease: Results From the Psychophysiological Investigations of Myocardial Ischemia Study

Depression is associated with increased risk of death among patients with coronary disease. Cardiovascular autonomic dysregulation may be one of the mechanisms by which depression exerts its effects on cardiovascular function. The purpose of this study was to determine whether depressive symptoms are associated with low heart rate variability (HRV) and prolonged HR recovery after exercise testing in patients with coronary artery disease (CAD). The Psychophysiological Investigation of Myocardial Ischemia (PIMI) was a large, multicenter study designed to assess psychological and physiological correlates of stress in patients with CAD. One hundred and eighty-eight patients with CAD as evidenced by at least 50% blockage of one major artery and a previous positive exercise stress test were included in this study. Patients included in this report were not taking beta blockers. Cardiovascular functioning was assessed by a modified Bruce protocol treadmill stress test. Measures of psychological functioning, including the Beck Depression Inventory (BDI), were also obtained. BDI scores were negatively correlated with HR recovery (r = -0.15, p = .04). Depression scores accounted for 3.5% of the variance in HR recovery when controlling for participant age (p < .01). Depressive symptoms were related to two HRV indices (ultra-low frequency, high frequency). Depressive symptoms are associated with cardiovascular autonomic nervous system dysfunction as assessed by HR recovery. This relationship is not merely due to an association of depression severity with beta blocker usage or a failure of depressed patients to achieve an adequate chronotropic response.

Differential endophenotypic markers of narcissistic and antisocial personality features: A psychophysiological investigation

This study investigated the differential psychophysiological correlates of narcissistic and antisocial personality features in a college student sample. Skin conductance (SC), respiratory sinus arrhythmia (RSA), and pre-ejection period (PEP) were monitored while participants watched a countdown to an aversive noise blast and viewed emotionally valenced slides. Results indicated that narcissistic personality features were unrelated to SC reactivity during the countdown, whereas antisocial personality features were negatively related to SC reactivity. Narcissistic personality features were also related to RSA decreases and PEP shortening while viewing happy slides, whereas antisocial personality features were not. Taken together, these findings suggest differential endophenotypic markers of narcissistic and antisocial personality features despite their clinical similarities.

Psychophysiological investigation of vigilance decrement: Boredom or cognitive fatigue?

The vigilance decrement has been described as a slowing in reaction times or an increase in error rates as an effect of time-on-task during tedious monitoring tasks. This decrement has been alternatively ascribed to either withdrawal of the supervisory attentional system, due to underarousal caused by the insufficient workload, or to a decreased attentional capacity and thus the impossibility to sustain mental effort. Furthermore, it has previously been reported that controlled processing is the locus of the vigilance decrement. This study aimed at answering three questions, to better define sustained attention. First, is endogenous attention more vulnerable to time-on-task than exogenous attention? Second, do measures of autonomic arousal provide evidence to support the underload vs overload hypothesis? And third, do these measures show a different effect for endogenous and exogenous attention? We applied a cued (valid vs invalid) conjunction search task, and ECG and respiration recordings were used to compute sympathetic (normalized low frequency power) and parasympathetic tone (respiratory sinus arrhythmia, RSA). Behavioural results showed a dual effect of time-on-task: the usually described vigilance decrement, expressed as increased reaction times (RTs) after 30 min for both conditions; and a higher cost in RTs after invalid cues for the endogenous condition only, appearing after 60 min. Physiological results clearly support the underload hypothesis to subtend the vigilance decrement, since heart period and RSA increased over time-on-task. There was no physiological difference between the endogenous and exogenous conditions. Subjective experience of participants was more compatible with boredom than with high mental effort.

Specific cue reactivity on computer game-related cues in excessive gamers.

It has been posited that excessive computer game playing behavior, referred to as computer game addiction, meets criteria that have been internationally established to define drug addiction. Nevertheless, there have been no psychophysiological investigations of the underlying mechanisms available to support the characterization of excessive computer gaming as behavioral addiction. To investigate whether excessive computer gaming parallels learning processes in development and maintenance (which are assumed to underlie drug addiction), the authors obtained a psychophysiological assessment of the (learned) emotional processing of computer game-relevant and -irrelevant cues. For this purpose, electroencephalographic recordings in excessive and casual computer game players were conducted. Significant between-group differences in event-related potentials evoked by computer game related-cues were found at parietal regions and point to an increased emotional processing of these cues in excessive pathological players compared with casual players. These results are in concordance with the suggestion that addiction is characterized and maintained through sensitization of the mesolimbic dopaminergic system along with incentive salience of specific addiction-associated cues.

A psychophysiological investigation of emotional processing in subjects with panic disorder

A psychophysiological investigation of emotional processing in subjects with panic disorder

Auditory Startle Response in Firefighters Before and After Trauma Exposure

Although previous psychophysiological studies have revealed heightened muscular and autonomic responses in individuals with posttraumatic stress disorder (PTSD), these studies have not permitted inferences about whether the abnormal responses are a vulnerability factor or are acquired following trauma. The present study reports the first prospective psychophysiological investigation, to the authors' knowledge, of posttraumatic stress responses by prospectively evaluating the auditory startle response in firefighters before and after trauma exposure. Orbicularis oculi (eye blink) electromyograms and skin conductance responses to 15 100-dB acoustic startle stimuli were assessed in 84 trainee firefighters before trauma exposure. After commencement of active duty, 35 firefighters were reassessed within 4 weeks of exposure to a traumatic event, and 36 firefighters were reassessed as a comparison group that was not exposed to trauma. In the trauma-exposed group, pretrauma physiological activity was predictive of posttrauma acoustic startle responses. Pretrauma skin conductance response to startle was also predictive of posttraumatic stress severity. These results provide initial support for elevated startle response being a vulnerability factor for posttraumatic stress responses.

Lateralization of pupillary light reflex parameters

Objective The aim of this study was to determine differing reactions of the left and right eyes with regard to pupillary light reflex (PLR) parameters. Methods All together 90 healthy subjects were included. In the first test series, 34 subjects were investigated on both eyes (left eye was tested first, three tests per day and one reliability test). In the second test series, 32 subjects were studied while changing the beginning side. In the last test series, 29 subjects were investigated 12 times each within 1 h (beginning side changed, without spoken advice). Infrared pupillometry was used to study pupil diameter, latency time, relative amplitude, contraction/dilation velocity, and pupil redilation time. Results The study demonstrated significant differences of PLR parameters between both eyes. In contrast to the pupil diameter of the left eye the papasympathetically-dominated right eye was not influenced by vocal instructions or by changing the beginning side. Conclusions PLR parameters might indicate functional lateralization of autonomic function in the central nervous system. High sensitivity of the procedure (arousal due to spoken advice, time of day) is advantageous for various psychophysiological investigations. Significance Differences between both eyes might point towards cortical lateralization of central autonomic function.

P.6.074 A psychophysiological investigation into violence and mental illness

Male rats receiving acrylamide (ACR) in their drinking water (100 ppm) for a six-week period displayed increased psychomotor stimulation to d-amphetamine (d-A; 1.0 mg/kg SC) under several conditions of handling and drug administration. Following behavioral tests a subset of the animals was sacrificed at 15, 50, 80 and 120 minutes following d-A and the brains removed and dissected for determinations of regional brain levels of several monoamine neurotransmitters and metabolits. ACR rats had elevated levels of 5-hydroxyindoleacetic acid (5-HIAA) in the striatum, septal area, and thalamus. The effect was most pronounced at 15 minutes post-drug with ACR rats not demonstrating a depression in 5-HIAA levels present in controls. Increases in accumben's dopamine and norepinephrine levels, evident after d-A, were of lesser magnitude in ACR-exposed rats. Decreases in dihydroxyphenylacetic acid and homovanillic acid, also evident after d-A, persisted for a longer duration in ACR-exposed rats. Light and electron microscopy of spinal cord, stiratum, nucleus accumbens and thalamus did not reveal morphologic abnormalities. Sciatic nerves showed histopathological changes characteristic of multi-focal dying-back peripheral nerve degeneration. It was concluded that acrylamide's effect on the psychomotor stimulant properties of d-A may be related to changes in a serotonergic inhibitory system.

Lateralization of Pupillary Light Reflex Parameters

Objective: The aim of this study was to determine differing reactions of the left and right eyes with regard to pupillary light reflex (PLR) parameters. Methods: All together 90 healthy subjects were included. In the first test series, 34 subjects were investigated on both eyes (left eye was tested first, three tests per day and one reliability test). In the second test series, 32 subjects were studied while changing the beginning side. In the last test series, 29 subjects were investigated 12 times each within 1 h (beginning side changed, without spoken advice). Infrared pupillometry was used to study pupil diameter, latency time, relative amplitude, contraction/dilation velocity, and pupil redilation time. Results: The study demonstrated significant differences of PLR parameters between both eyes. In contrast to the pupil diameter of the left eye the papasympathetically-dominated right eye was not influenced by vocal instructions or by changing the beginning side. Conclusions: PLR parameters might indicate functional lateralization of autonomic function in the central nervous system. High sensitivity of the procedure (arousal due to spoken advice, time of day) is advantageous for various psychophysiological investigations. Significance: Differences between both eyes might point towards cortical lateralization of central autonomic function. q 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

The startle reflex in schizophrenia: habituation and personality correlates.

Schizophrenia has long been associated with abnormal patterns of arousal that are thought to reflect disturbances in the reticular-activating system of the brain. Psychophysiological investigations of sensory responsivity have repeatedly demonstrated reduced reactivity and habituation to moderately intense stimuli in patients with schizophrenia. While not traditionally used as a measure of physiological arousal, the startle reflex represents an alternative method for studying reactivity and habituation in schizophrenia. This study examined eye blink responsivity to a repeatedly presented intense acoustic startle probe in men with chronic schizophrenia and healthy normal controls. Subjects' personality profiles were also measured, as increased reactivity and arousal have been traditionally implicated as a physiological component to the personality trait of neuroticism. Results indicated that schizophrenic subjects did demonstrate significantly reduced rates of habituation to the acoustic startle probe and higher scores on measures of neuroticism in comparison to normal controls. However, no correlation between habituation rate and neuroticism emerged. These studies replicate previous findings of habituation in schizophrenia and provide further evidence for sensory reactivity disturbances in schizophrenia. The relationship of these findings to cognitive disturbances in schizophrenia is considered and directions for future research are discussed.

Brain polarization in humans: a reappraisal of an old tool for prolonged non-invasive modulation of brain excitability.

Direct current (DC) is very effective in modulating spontaneous neuronal firing. The history of electrophysiology starts with the discovery of the biological effects of DC and as early as two centuries ago scalp DC was used to treat mental disorder. Psychophysiological investigations suggested a possible effect of scalp DC in humans. More recently several studies assessed, with motor potentials evoked by transcranial brain stimulation, the motor-cortical excitability changes induced by scalp DC. Even weak DCs pass through the scalp and influence human brain activity. DCs delivered at relatively strong intensities (1 mA) and for long periods (10 min or so), not only influence (either increase or decrease) brain excitability during their application in normal subjects, but induce persistent changes in excitability after their offset that, at least in the motor cortex, can last for almost 1 h. Scalp DC might represent a non-invasive simple and valuable potential treatment for psychiatric and neurologic diseases with changes in brain excitability or focally abnormal (increased or decreased) function.