Event-related EEG theta and alpha band oscillatory responses during language translation

Recent investigations on oscillatory EEG dynamics by means of event-related synchronisation and desynchronisation (ERS/ERD) suggest that first language semantic information processing is primarily reflected in the theta (4-7 Hz) and alpha (7-13 Hz) frequency bands. In this pilot study we explore whether similar ERS/ERD patterns emerge during language translation and which frequency bands sensitively respond to the difficulty of translation and the translation success. Thirteen female students of translation and interpreting were visually presented high and low frequency English words that had to be translated into German. Time-frequency representations of ERS/ERD between 2 and 50 Hz displayed a theta ERS response about 200-600 ms after word presentation, a beta ERD from about 400 ms, and alpha ERS and ERD patterns about 200-400 ms after word presentation. Statistical analyses of the ERS/ERD data in the theta (4-7 Hz), two alpha frequency bands (7-10 Hz and 10-13 Hz), and a beta band (20-30 Hz) predominantly revealed: (a) higher parietal theta ERS and frontal upper alpha ERD during the translation of low as compared to high frequency words, and (b) generally stronger ERD in the lower alpha band and larger left-hemispheric upper alpha ERD for successfully translated in contrast to not translated low frequency words. These findings provide first evidence of the sensitivity of the theta and alpha ERS/ERD measure to lexical-semantic processes involved in language translation.     

Brain oscillatory responses during the different stages of an auditory memory search task in children

We assessed brain oscillatory responses of the 4-30 Hz electroencephalographic frequency bands in children (mean age 13 years) during the different stages of an auditory memory search, namely the encoding of four words and recognition of the positive and negative probe words. In children, theta (approximately 4-6 Hz) electroencephalographic responses during recognition were of greater magnitude than those during encoding and alpha (approximately 8-12 Hz) event-related synchronization responses during encoding increased with increasing memory load. During recognition, greater magnitude alpha and beta (>12 Hz) event-related desynchronization responses were observed during the presentation of the positive probe as compared with the negative. Complex patterns of theta, alpha and beta frequency brain oscillatory responses during auditory information processing are present already in children of age approximately 13 years.     

Creativity related cortex activity in the remote associates task

The involvement of different oscillating neuronal systems during verbal creative thinking was investigated by multi-channel EEG measuring. The remote associates task (RAT) as a model of creative thinking in comparison to the resting condition and the simple associates task (SAT) was used. The EEG coherence along with spectral power density estimates were evaluated in each of the six frequency bands in 4-30 Hz range. We have found out RAT-related EEG changes mainly in the theta1, alpha1, alpha2 and beta2 bands. The RAT-induced cortical activation was differed from the SAT-induced EEG pattern by (i) widespread enhancement of power and coherence in the beta2, (ii) the theta1 power increase in the frontal cortex, and (iii) increased desynchronization of the alpha1,alpha2 mainly over posterior cortex together with the alpha1 coherence decrease in the prefrontal sites. Originality scores of the verbal associates positively correlated with an increase of coherence focused in the fronto-parietal regions of both hemispheres in the beta2 and in the left parieto-temporal loci in the alpha1. Additionally, more original responses positively correlated with amplitude of the alpha1 mostly in the left hemisphere. We propose that widespread cortical integration of multi-component internal processing has been simultaneously mediated during creative verbal thinking. The selectively distributed theta, alpha, and beta oscillations reflect intra- and inter-hemispheric communication networks with different functional relations to the RAT solving. The theta1 and alpha1 rhythms seem to specifically relate to top-down information processing such as deliberate sustained attention and working-memory-retention during defocused attention, respectively, whereas larger interregional synchrony in the beta2 band may mediate 'differential' attention to diffusely activating alternative meanings of words and remote associates from coarse semantic coding.     

Distinction between perceptual and attentional processing in working memory tasks: a study of phase-locked and induced oscillatory brain dynamics

Working memory involves the short-term storage and manipulation of information necessary for cognitive performance, including comprehension, learning, reasoning and planning. Although electroencephalogram (EEG) rhythms are modulated during working memory, the temporal relationship of EEG oscillations with the eliciting event has not been well studied. In particular, the dynamics of the neural network supporting memory processes may be best captured in induced oscillations, characterized by a loose temporal link with the stimulus. In order to differentiate induced from evoked functional processes, the present study proposes a time-frequency analysis of the 3 to 30 Hz EEG oscillatory activity in a verbal n-back working memory paradigm. Control tasks were designed to identify oscillatory activity related to stimulus presentation (passive task) and focused attention to the stimulus (detection task). Evoked theta activity (4-8 Hz) phase-locked to the visual stimulus was evidenced in the parieto-occipital region for all tasks. In parallel, induced theta activity was recorded in the frontal region for detection and n-back memory tasks, but not for the passive task, suggesting its dependency on focused attention to the stimulus. Sustained induced oscillatory activity was identified in relation to working memory in the theta and beta (15-25 Hz) frequency bands, larger for the highest memory load. Its late occurrence limited to nonmatched items suggests that it could be related to item retention and active maintenance for further task requirements. Induced theta and beta activities displayed respectively a frontal and parietal topographical distribution, providing further functional information on the fronto-posterior network supporting working memory.     

Oscillatory activity during maintenance of spatial and temporal information in working memory

Working memory (WM) processes help keep information in an active state so it can be used to guide future behavior. Although numerous studies have investigated brain activity associated with spatial WM in humans and monkeys, little research has focused on the neural mechanisms of WM for temporal order information, and how processing of temporal and spatial information might differ. Available evidence indicates that similar frontoparietal regions are recruited during temporal and spatial WM, although there are data suggesting that they are distinct processes. The mechanisms that allow for differential maintenance of these two types of information are unclear. One possibility is that neural oscillations may differentially contribute to temporal and spatial WM. In the present study, we used scalp electroencephalography (EEG) to compare patterns of oscillatory activity during maintenance of spatial and temporal information in WM. Time-frequency analysis of EEG data revealed enhanced left frontal theta (5–8 Hz), enhanced posterior alpha (9–12 Hz), and enhanced left posterior beta (14–28 Hz) power during the delay period of correct temporal order trials compared to correct spatial trials. In contrast, gamma (30–50 Hz) power at right lateral frontal sites was increased during the delay period of spatial WM trials, as compared to temporal WM trials. The present results are consistent with the idea that neural oscillatory patterns provide distinct mechanisms for the maintenance of temporal and spatial information in WM. Specifically, theta oscillations are most critical for the maintenance of temporal information in WM. Possible roles of higher frequency oscillations in temporal and spatial memory are also discussed.     

The relationship between brain oscillations and BOLD signal during memory formation: a combined EEG-fMRI study

Previous studies demonstrated that increases in the theta frequency band with concomitant decreases in the alpha/beta frequency band indicate successful memory formation. However, little is known about the brain regions and the cognitive processes that underlie these encoding-related oscillatory memory effects. We investigated this relationship using simultaneous EEG-fMRI recordings in humans during long-term memory encoding. In line with prior studies, we demonstrate that a decrease in beta power and an increase in theta power positively predict subsequent recall. In fMRI, stronger activity in the left inferior prefrontal cortex and the right parahippocampal gyrus correlated with successful memory formation. EEG source localization revealed that the subsequent memory effect in the beta band was localized in the left inferior prefrontal cortex, whereas the effect in the theta band was localized in medial temporal lobe regions. Trial-by-trial correlations between EEG and BOLD activity showed that beta power correlated negatively with left inferior prefrontal cortex activity. This correlation was more pronounced for items that could later be successfully recalled compared to items later forgotten. Based on these findings, we suggest that beta oscillations in the left inferior prefrontal cortex indicate semantic encoding processes, whereas theta oscillations in the medial temporal lobe reflect the binding of an item to its spatiotemporal context.     

EEG effect of basal forebrain neuropeptide Y administration in urethane anaesthetized rats

Neuropeptide Y (NPY) is present both in local neurons as well as in fibers in the basal forebrain (BF), an area that plays an important role in the regulation of cortical activation. In previous studies, NPY axons were found to innervate corticopetal cholinergic cells in this area. In addition, identified NPY positive neurons have been shown to be silent during cortical activation, but active during slow EEG waves. However, no in vivo studies have shown the effect of local NPY release in the BF on the EEG. In the present experiments, the EEG was examined following NPY injection (0.5 microl, 300-500 pmol) into the BF of urethane-anaesthetized rats. Fronto-parietal EEG was recorded on both sides and relative EEG power was calculated in the delta (0-3 Hz), theta (3-9 Hz), alpha (9-16 Hz) and beta (16-48 Hz) frequency bands. We found a significant increase in relative delta power and a decrease in the power of all higher frequency bands (theta, alpha, beta) after NPY injection. These results suggest that NPY can inhibit cortical activation via the BF.     

Computed EEG topography of response to visual and auditory stimuli

EEG activity was monitored in 15 normal subjects at rest and while they were given 10 sec continuous light or tone stimuli of different intensities. Topographical cortical changes were assessed using 16-channel EEG power estimate maps of the left hemisphere. Statistical analyses were performed using analyses of variance and t test, and the reactivity of the EEG, i.e., the percent change from the baseline state, in response to stimulation, was topographically mapped. Significant EEG reactivity was recorded in alpha, theta and delta bands without modification in the beta band. Stimulation-induced effects were maximum in the posterior part of the brain for both tone and light. The light effect was stronger than tone in the alpha band, but no differences in modality effect were recorded in the delta or theta band. Analysis of frequency bands within the alpha and theta band revealed a different pattern of reactivity with different regional involvements for tone and light. EEG reactivity occurred mainly in 7-10 Hz frequency bands with no significant change in 5, 6, 11, 12 and 13 Hz. Reactivity was maximal in the temporal area during tone for 7-9 Hz and in the occipital region during light for 8-10 Hz. The 8 and 9 Hz frequency bands showed increased blocking with an increase in stimulus intensity. Taken together, the results indicate that visual and auditory stimuli both produce an EEG amplitude decrease which is greatest over their respective primary sensory cortex.     

Human cortical theta reactivity to high-frequency repetitive transcranial magnetic stimulation

Electroencephalography (EEG) can directly monitor the temporal progression of cortical changes induced by repetitive Transcranial Magnetic Stimulation (rTMS) and facilitate the understanding of cortical and subcortical influences in the genesis of oscillations. In this combined rTMS/EEG study, we aimed to investigate changes in oscillatory activity after high-frequency (～11 Hz) rTMS relative to the number of applied pulses. Twenty intermittent trains of 20 or 60 rTMS pulses were delivered over the human primary motor cortex at rest and tuned to individual mu frequency. The regional and interregional oscillatory neural activity after stimulation were evaluated using event-related power (ERPow) and event-related coherence (ERCoh) transformations. The most prominent changes for ERPow were observed in the theta band (4-7 Hz), as an increase in ERPow up to 20 s following 60 rTMS pulses, whereas ERPow increases were smaller in mu (10-12 Hz) and beta (13-30 Hz). ERCoh revealed that rTMS 60 modulated the connectivity in the theta band for up to 20 s. The topography of mu and theta changes were not identical; mu was more focal and theta was more global. Our data suggested the presence of independent cortical theta and mu generators with different reactivity to rTMS but could not rule out possible thalamocortical contributions in generating theta and mu over the motor network.     

Oscillatory correlates of retrieval-induced forgetting in recognition memory

Retrieval practice on a subset of previously studied material enhances later memory for practiced material but can inhibit memory for related unpracticed material. The present study examines the effects of prior retrieval practice on evoked (ERPs) and induced (oscillatory power) measures of electrophysiological activity underlying recognition of practiced and unpracticed words. Compared to control material, recognition of unpracticed words was characterized by reduced amplitudes of the P2 ERP component and by reduced early (200-400 msec) oscillatory theta power. The reduction in P2 amplitude was associated with decreased evoked theta power but not with decreased theta phase locking (phase-locking index). Recognition of unpracticed material was further accompanied by a reduction in occipital gamma power (>250 msec). In contrast, the beneficial effects of retrieval practice on practiced words were reflected by larger parietal ERP positivity (>500 msec) and by a stronger decrease in oscillatory alpha power in a relatively late time window (>700 msec). The results suggest that the beneficial and detrimental effects of retrieval practice are mediated by different processes. In particular, they suggest that reduced theta (4-7 Hz) and gamma (60-90 Hz) power reflect the specific effects of inhibitory processes on the unpracticed material's memory representation.     

EEG spectral characteristics following ethanol administration in young men

The effects of consumption of low doses of ethanol (0.75 mg/kg) on spectral components of the EEG were investigated in 24 21-25-year-old males. A comparison of mean spectral power in 4 frequency bands (4-7 Hz, 7.5-9 Hz, 9-12 Hz, and 12-20 Hz) at 90 min post consumption revealed that ethanol, as opposed to placebo, significantly increased power in the two slower frequency bands, in both posterior and anterior leads. A reduction in the frequency at which power values peaked in the theta (4-7 Hz), fast alpha (9-12 Hz), and beta (12-20 Hz) frequency ranges was also seen following ethanol consumption. The ethanol induced lowering of peak power in the fast alpha range was observed in all 4 leads (F4-C4, P4-O2, F3-C3, and P3-O1), whereas the frequency changes in the theta and beta frequencies were only significant in a frontal lead. Ethanol was also noted to produce a decrease in the stability of the EEG in the fast alpha band as quantified by the coefficient of variation of power. Subjective response to ethanol was observed to vary depending on the subjects' pre-drug EEG pattern. Men with high amounts of fast alpha activity at baseline, in lead P4-O2, reported feeling less 'high' and less overall feelings of intoxication after ethanol than the men with lower amounts of pre-drug fast alpha waves. In addition, subjects were sorted into 'low' and 'moderate' drinkers depending on their quantity and frequency of drinking over the previous 6 month period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spectral-temporal analysis of cortical oscillations during lexical processing

We investigated the oscillatory neural correlates of auditory lexical processing in healthy adults. Synthetic aperture magnetometry was used to characterize the timing of event-related desynchronization (ERD)/event-related synchronization (ERS) in superior temporal gyri following low-frequency and high-frequency words in contrast to nonwords. ERS and ERD responses were found with both word and nonword stimuli. Analysis of power revealed significantly elevated θ-α range (6-14 Hz) ERD in response to words compared with nonwords (left hemisphere: 390-945 ms poststimulus). Furthermore, a burst of ERS in the γ band (40-50 Hz, centered at 410 ms poststimulus) distinguished high-frequency and low-frequency words, and also displayed left-hemispheric enhancement following words. Results demonstrate a clear neural correlate of lexical access and provide a basis for further study of spectral-temporal brain activity during language processing.     

Acute modulation of cortical oscillatory activities during short trains of high-frequency repetitive transcranial magnetic stimulation of the human motor cortex: a combined EEG and TMS study

In this study, a combined repetitive transcranial magnetic stimulation/electroencephalography (rTMS/EEG) method was used to explore the acute changes of cortical oscillatory activity induced by intermittent short trains of high-frequency (5-Hz) rTMS delivered over the left primary motor cortex (M1). We evaluated the electrophysiological reaction to magnetic stimulation during and 2-4 s after 20 trains of 20-pulses rTMS, using event-related power (ERPow) that reflects the regional oscillatory activity of neural assemblies, and event-related coherence (ERCoh) that reflects the interregional functional connectivity of oscillatory neural activity. These event-related transformations were for the upper alpha (10-12 Hz) and beta (18-22 Hz) frequency ranges, respectively. For the alpha band, threshold rTMS and subthreshold rTMS induced an ERPow increase during the trains of stimulation mainly in frontal and central regions ipsilateral to stimulation. For the beta band, a similar synchronization of cortical oscillations for both rTMS intensities was seen. Moreover, subthreshold rTMS affected alpha-band activity more than threshold rTMS, inducing a specific ERCoh decrease over the posterior regions during the trains of stimulation. For beta band, the decrease in functional coupling was observed mainly during threshold rTMS. These findings provide a better understanding of the cortical effects of high-frequency rTMS, whereby the induction of oscillations reflects the capacity of electromagnetic pulses to alter regional and interregional synaptic transmissions of neural populations.     

Modality matters: the effects of stimulus modality on the 4- to 30-Hz brain electric oscillations during a lexical decision task

The aim of the current study was to assess modality-specific brain oscillatory responses during cognitive processing. Brain oscillatory ERD/ERS responses of the 4- to 30-Hz EEG frequency bands were examined during lexical decision where the task is to identify whether the presented stimulus is a word or a pseudoword. Seven subjects performed the task with visual stimuli and twelve subjects with auditory stimuli. Visual stimuli elicited greater theta ERS responses as compared to the auditory stimuli. Both stimulus modalities elicited alpha and beta frequency ERD, these being greater for the auditory stimuli. Auditory stimuli elicited also later emerging beta ERS responses, absent for the visual stimuli. The lexicality effects (words vs. pseudowords) were greater for the auditory than for the visual stimuli. When studying brain oscillatory correlates of cognitive processing, the stimulus modality matters. Some effects may arise and some vanish depending on in which modality a cognitive experiment is being conducted.     

Power spectral density changes and language lateralization during covert object naming tasks measured with high-density EEG recordings

Our objective was to study changes in EEG time-domain power spectral density (PSDt) and localization of language areas during covert object naming tasks in human subjects with epilepsy. EEG data for subjects with epilepsy were acquired during the covert object naming tasks using a net of 256 electrodes. The trials required each subject to provide the names of common objects presented every 4 seconds on slides. Each trial comprised the 1.0 second before and 3.0 seconds after initial object presentation. PSDt values at baseline and during tasks were calculated in the theta, alpha, beta, low gamma, and high gamma bands. The spatial contour plots reveal that PSDt values during object naming were 10-20% higher than the baseline values for different bands. Language was lateralized to left frontal or temporal areas. In all cases, the Wada test disclosed language lateralization to the left hemisphere as well.     

Spatiotemporal changes of EEG activity during waking-sleeping transition period

To evaluate the spatiotemporal changes of EEG during waking-sleeping transition or hypnagogic period, spectral analysis of the five scalp EEG on the midline (Fpz, Fz, Cz, Pz and Oz) referenced to the left ear lobe was carried out on seven young male subjects. Power spectra from consecutive samples of 5.12 sec period with 0.2 Hz resolution were studied from 10 min before the manually scored stage 1 onset to 30 min after the onset of stage 1. The average power spectra over 1 min segments and corresponding coefficient of variation (CV) were determined for the frequency bands of delta (1-3 Hz), theta (4-7 Hz), alpha (8-12 Hz), sigma (13-15 Hz) and beta (16-19 Hz). The latency score was defined as the time elapsed from the onset of stage 1 to the first epoch when the frequency band power, using the ANOVA significantly increased (or decreased) in comparison with the average level at the onset of stage 1. Median latency scores for each band were similar to the Cz scores, with a ranking, from early to late, of: alpha (2 min), theta (3 min), delta (5 min) and sigma (5 min). Significant change was not observed on the beta band activity. In terms of the EEG areas, the shortest latency was found in the theta band activity of the Fz EEG (2 min), and the longest was the sigma band activity of the Fpz and Oz EEG (8 min). The average stage 2 latency was 3.5 min when it was measured as time elapsed between the onset of stage 1 and 2. The average curves of delta, theta and alpha band CVs, started to increase just before or immediately after stage 1 onset and continued to increase for about 10 min. If the increased CV or unsteadiness of EEG activity is taken as a characteristic of the hypnagogic period, hypnagogic states may be considered to have continued until about 10 min after the stage 1 onset. Delta-theta activity showed a rapid rise in power after the onset of stage 1 for all areas. Delta power at the occipital, however, increased more gradually, and consistently remained at a lower level. The differences of delta power between Oz and other four electrode sites became clear at 7 min after the onset of stage 1. These regional differences may reflect the termination of hypnagogic effects.(ABSTRACT TRUNCATED AT 400 WORDS)     

Topographic brain mapping of EEG before and after open-heart surgery

The brain function of 60 patients undergoing open-heart surgery (36 patients receiving coronary artery bypass, 21 patients valve replacements, 3 both) was investigated before and 10 days after the operation utilizing topographic brain mapping of the electroencephalogram (EEG). The postoperative EEG changes were characterized by a slight delta-theta increase, an alpha decrease [especially in the fast alpha (10.5-13 Hz) band] and a beta increase in the relative power. The total power and the absolute power of the delta-theta, alpha and beta showed a decrease, the dominant frequency a significant slowing from 9.7 to 9.3 Hz. The centroid of alpha and beta activity decreased as well. These results are similar to findings obtained in patients with organic brain syndrome. The EEG changes were prominent over the left hemisphere, which may be of particular clinical relevance.     

Free copper and resting temporal EEG rhythms correlate across healthy, mild cognitive impairment, and Alzheimer's disease subjects.

OBJECTIVE: The present study tested the hypothesis that the serum copper abnormalities were correlated with alterations of resting electroencephalographic (EEG) rhythms across the continuum of healthy elderly (Hold), mild cognitive impairment (MCI), and AD subjects. METHODS: Resting eyes-closed EEG rhythms delta (2-4Hz), theta (4-8Hz), alpha 1 (8-10.5Hz), alpha 2 (10.5-13Hz), beta 1 (13-20Hz), beta 2 (20-30Hz), and gamma (30-40Hz), estimated by LORETA, were recorded in 17 Hold, 19 MCI, 27 AD- (MMSE< or =20), and 27 AD+ (MMSE20) individuals and correlated with copper biological variables. RESULTS: Across the continuum of Hold, MCI and AD subjects, alpha sources in parietal, occipital, and temporal areas were decreased, while the magnitude of the delta and theta EEG sources in parietal, occipital, and temporal areas was increased. The fraction of serum copper unbound to ceruloplasmin positively correlated with temporal and frontal delta sources, regardless of the effects of age, gender, and education. CONCLUSIONS: These results sustain the hypothesis of a toxic component of serum copper that is correlated with functional loss of AD, as revealed by EEG indexes. SIGNIFICANCE: The present study represents the first demonstration that the fraction of serum copper unbound to ceruloplasmin is correlated with cortical delta rhythms across Hold, MCI, and AD subjects, thus unveiling possible relationships among the biological parameter, advanced neurodegenerative processes, and synchronization mechanisms regulating the relative amplitude of selective EEG rhythms.     

Valproate decreases EEG synchronization in a use-dependent manner in idiopathic generalized epilepsy.

INTRODUCTION: In order to explore the mechanism of action of valproate (VPA) in idiopathic generalized epilepsy (IGE), the effect of VPA on cortical EEG activity was investigated. Hypothesis: VPA decreases EEG synchronization in the delta and theta frequency bands in a use-dependent manner in IGE patients. METHODS: First setting: EEG records of 17 untreated IGE patients (NAE group) were analyzed and compared to those of 15 healthy controls (NC group). Second setting: EEG recorded in the untreated condition (NAE) was compared to the EEG recorded in the treated condition (VPA) of the patient group. Technique and analysis: 2 min of eyes-closed, waking EEG background activity (without epileptiform potentials and artifacts) were analyzed. Absolute power (AP) and mean frequency (MF) were computed for 19 electrodes and four frequency bands (delta=1.5-3.5 Hz, theta=3.5-7.5 Hz, alpha=7.5-12.5 Hz, beta=12.5-25.0 Hz). Log-transformed data entered further analysis. Group differences were computed by means of parametric statistics including correction for multiple comparisons. The VPA-related changes (APvpa-APnae) were correlated with the degree of the baseline abnormality (APnae) and the daily dose/serum levels of VPA. MAIN RESULTS: Statistically significant (p<0.05, corrected) changes in the first setting: diffuse delta, theta, alpha AP increase, mainly right hemispheric beta AP increase was found in the NAE group, as compared to the NC group. Second setting: VPA decreased delta and theta AP. Strong correlation was demonstrated between the degree of the initial AP abnormality and the VPA-related AP decrease. AP decrease did not correlate with the daily dose and the serum level of the drug. CONCLUSION: The hypothesis that VPA decreased EEG synchronization in the delta and theta frequency bands in a use-dependent manner was supported. The findings contribute to the understanding of the action of VPA at the network level.     

A comparison between spontaneous electroencephalographic activities induced by morphine and morphine-related environment in rats

Previous studies demonstrated that drug cues could elicit drug-like or withdrawal-like effect, both subjectively and physiologically. However, few studies have compared the central activities induced by a drug-related environment and the drug itself. The aim of this study was to observe and compare electroencephalographic (EEG) changes induced by acute morphine administration and by the morphine-related environment. EEG activities were recorded via twelve skull electrodes scattered on the left and right cortex in conscious, freely moving rats, either after acute morphine administration or after successful training of conditioned place preference. Acute administration of morphine (0.1, 0.5, 1, 5, 10, 20 mg/kg, i.p.) produced an increase in absolute EEG power in the delta, theta, alpha1, alpha2, beta1, and beta2 bands, as well as a decrease in the gamma band. Topographic mapping revealed a maximal increase in the lateral leads in the theta band and a maximal change in the centro-frontal region in the remaining bands. After place conditioning training, the morphine-related environment induced a diffuse decrease in absolute power in the delta, theta, alpha1, alpha2, beta1, and beta2 bands, which was opposite to the changes induced by acute morphine administration. In addition, the changes in relative power induced by the two situations also diverged. These results indicate that the central mechanisms underlying the motivation of morphine-induced place preference may be somehow different from those underlying the reward effects produced by acute morphine administration.