Brain Electric Field Research Articles

Topographic change of ERP due to discrimination of CV syllables with various vowel durations

This study aims to investigate the cerebral process of discrimination of consonant–vowel (CV) syllables differing in vowel length. The subjects were normal adults. A single human CV syllable (/ma/) and five variants with reduced vowel duration were used as stimuli. EEGs were recorded from 16 scalp locations under the following two conditions: (1) ignore condition: subjects heard stimulus sounds while relaxing and (2) discriminate condition: subjects were asked to discriminate unreduced CV syllable (/ma/) as a target and press the button when they detected it. Regardless of the vowel lengths of the CV syllable, P2 and P3 components were observed in both conditions. With the reduction of the vowel duration, the scalp distributions of P2 shifted from anterior to vertex in the ignore condition and from posterior to vertex in the discriminate condition. Therefore, not only vowel duration but also the task condition affected the generators of the P2 component. Vowel duration also affected the generator of the P3 component. In the ignore condition, the unreduced CV syllable evoked an anterior positive, and CV syllables with reduced vowels evoked posterior positive P3s. However, in the discriminate condition, the P3 component was anterior-negative/posterior-positive distributed as long as the CV syllable was perceived as /ma/. Therefore, the brain electrical fields of the P3 component might reflect cortical discrimination in the categorical hearing of human CV syllables.

Topographic changes of ERP during a CPT-AX task at pre- and post-medication of methylphenidate in children with ADHD

To examine cerebral process of motor control in children with Attention-Deficit/Hyperactivity Disorder (ADHD; mean age, 11 years), event-related potentials (ERPs) during a cued continuous performance test (CPT-AX) were recorded from ADHD children an hour after psychostimulant (methylphenidate) dosage (Medicated ADHD), and without psychostimulants (Non-Medicated ADHD). These data were compared with ERPs in unmedicated age-matched normal controls (Non-ADHD). Hit rate in Non-medicated ADHD was significantly lower than that in Non-ADHD. However, their performance improved significantly due to psychostimulant medication, up to levels comparable to those of Non-ADHD subjects. In the ERP elicited by nontargets, P2 amplitudes in Non-Medicated ADHD were smaller than in Non-ADHD. Due to medication, P2 amplitudes increased and became comparable to that in Non-ADHD. Medication also improved a delayed onset of the P2 brain electric field in ADHD. Reduced amplitude of ERP in Non-Medicated ADHD suggests a lower activation at this relatively early stage of visual information processing in ADHD. In contrast, enhancement of ERP in Medicated ADHD implies that the medication contributes to allocate resources for orienting their attention to distinguish stimulus relevance, and to inhibit later processing of irrelevant stimuli properly. These results imply that methylphenidate improves response control in ADHD.

Global field power and low resolution electromagnetic tomography solutions in Alzheimer's disease

Brain electrophysiological characteristics of Alzheimer's disease (AD) were investigated by global field power (GFP) and low-resolution electromagnetic tomography (LORETA). GFP measures the energy of the brain electric field. LORETA computes for the smoothest of all possible source configurations throughout the brain volume by minimizing the total source strengths. The study population included a total of 29 AD patients and 15 age-matched controls. Clinical stages were based on the functional assessment staging (FAST). Mild-AD consists of 18 patients with a diagnosis of moderate cognitive decline (Stage 4). Advanced-AD consists of 11 patients with a diagnosis of severe cognitive decline (Stages 5, 6 and 7). Nineteen-channel eye-closed EEG was recorded using Cz reference and artifact-free 20 s were picked up and recomputed vs. average reference. Mild-AD showed lower power at Beta-2 and Beta-3 bands than control, and remarkably, advanced-AD showed lower power at the higher band of Alpha-1 than control. The t-scores of the current density of mild-AD were more reduced in the right frontal and temporal areas than the control at the beta bands, and of advanced-AD, reduced in low temporal area at alpha bands and reduced in temporal and parietal area at beta bands. This result clearly demonstrates the physiological characteristics of the clinical stages in Alzheimer's disease.

Cognitive response control in writer's cramp.

Disturbances of the motor and sensory system as well as an alteration of the preparation of movements have been reported to play a role in the pathogenesis of dystonias. However, it is unclear whether higher aspects of cortical - like cognitive - functions are also involved. Recently, the NoGo-anteriorization (NGA) elicited with a visual continuous performance test (CPT) during recording of a 21-channel electroencephalogram has been proposed as an electrophysiological standard-index for cognitive response control. The NGA consists of a more anterior location of the positive area of the brain electrical field associated with the inhibition (NoGo-condition) compared with that of the execution (Go-condition) of a prepared motor response in the CPT. This response control paradigm was applied in 16 patients with writer's cramp (WC) and 14 age matched healthy controls. Topographical analysis of the associated event-related potentials revealed a significant (P < 0.05) NGA effect for both patients and controls. Moreover, patients with WC showed a significantly higher global field power value (P < 0.05) in the Go-condition and a significantly higher difference-amplitude (P < 0.05) in the NoGo-condition. A source location analysis with the low resolution electromagnetic tomography (LORETA) method demonstrated a hypoactivity for the Go-condition in the parietal cortex of the right hemisphere and a hyperactivity in the NoGo-condition in the left parietal cortex in patients with WC compared with healthy controls. These results indicate an altered response control in patients with WC in widespread cortical brain areas and therefore support the hypothesis that the pathogenesis of WC is not restricted to a pure sensory-motor dysfunction.

A double-dissociation of English past-tense production revealed by event-related potentials and low-resolution electromagnetic tomography (LORETA)

Objectives: Evidence of systematic double-dissociations of neural activity associated with the generation of regular and irregular past tense in healthy individuals may prove decisive in distinguishing between single- and dual-route models of morphological processing, because the former (connectionist models of morphological processing) have only been able to simulate double-dissociations of past-tense morphology as low-probability phenomena. Methods: Twenty-eight channel event-related potentials (ERPs) were recorded in response to past-tense production and subsequently analyzed using a 3-stage strategy. Results: A data-driven algorithm temporally segmented the ERPs into 16 distinct epochs of stable field configuration (microstates). A space-oriented brain electric field analysis determined that one of those epochs, 288–321 ms after the verb stem presentation, showed significant differences between the regular and irregular verb conditions. As a further test of these results, a novel source localization technique that computes 3-dimensional distribution of cortical current density in the Talairach brain atlas – low-resolution electromagnetic tomography – found in the above microstate more activity for regulars in the right prefrontal and right temporal areas and for irregulars in the left temporal areas and the anterior cingulate cortex, which can be taken as evidence of systematic double-dissociation. Conclusions: The present results achieved with a source localization technique provide evidence of a two-way compartmentalization of neural activity corresponding to regular and irregular past tense, thus corroborating the dual-mechanism character of verb morphology.

Spatial Structure of Brain Electric Fields during Intermittent Photic Stimulation

EEG changes in 27 young healthy male right-handed volunteers on intermittent photic stimulation (IPS) were estimated using global field power (GFP), EEG microstate modeling and analysis (EMMA), and low-resolution electromagnetic brain tomography (LORETA). The GFP significantly increased at flashing frequency and high harmonics. Three model maps were extracted with the EMMA procedure, from which high alternation rates of each microstate were observed. Moreover, two of the three model maps contributed very highly, occurring most frequently. LORETA imaging of the three model maps obtained from the EMMA procedure showed that both visual dominant cortical areas were activated, especially in the left hemisphere. These results suggest that IPS does not cause peculiar spatial configurations of the brain electric field, but does cause acceleration and deviation of the microstate alternation. Also, a functional laterality between hemispheres might be enhanced by symmetric IPS.

Changes of the brain electrical fields during the continuous performance test in attention-deficit hyperactivity disorder-boys depending on methylphenidate medication

Objective: The continuous performance test (CPT) is successfully applied to evaluate attentional performance in attention-deficit hyperactivity disorder (ADHD)-children. The aim of the present study was to investigate the changes of the topographic P300-features in relation to methylphenidate-medication and to different attentional processes in primer- and distractor-conditions.Methods: Twenty-one-channel-ERPs of 17 ADHD-boys were analyzed with reference-independent methods. Four quasi stable microstates within the time frames of conventional P100, P200, P3a and P3b components were identified by means of a data-driven segmentation procedure.Results: In segment 3 topographical assessment yielded a significant occipital and right-shift of the positive centroid, longer centroid distance and higher amplitudes in primer- than in distractor conditions. MPH increased the amplitude and distance in primer and distractor-condition, without changing the topography. In segment 4 the electric fieldstrength of distractor-conditions collapsed, whereas the primer condition showed a strong fronto-parietallly oriented potential-field. There was a tendency to higher amplitudes due to MPH-medication.Conclusions: These results indicate a robust neurophysiologic differentiation of cognitive processes. MPH activates an early (P3a) covert attention process indicated by increased amplitudes and centroid. No effects were seen in later processes. Based on these effects, we propose to use the amplitude- and distance-increase in microstate 3 as an indicator of MPH efficacy in ADHD-boys.

Electrophysiological assessment of impulsive behavior in healthy subjects

The different concepts of impulsivity cover a wide range of divergent behaviors. In clinical terms, aspects of impulsivity are both an important feature in several psychiatric conditions related to a low central serotonergic neurotransmission like aggressive behavior and suicidality, and a core symptom of frontal lobe syndromes of various etiologies. Assessment of the different forms of impulsivity so far relies on clinical observations and self-rating questionnaires. Measurements of a distinct brain function associated with impulsive behavior are not available yet, however, electrophysiological parameters of cognitive response control elicited with the execution (Go-condition) and the inhibition (NoGo-condition) of a prepared motor response within the Continuous Performance Test (CPT) might be suitable candidates. By means of a spatial analysis method the centers of gravity (centroids) of the brain electrical fields evoked with Go- and NoGo-responses can be localized and quantified. In the present study, the Go- and NoGo-centroids and the impulsivity score in Eysenck's I 7-scale were determined in 22 healthy subjects (10 women, 12 men, mean age 42.0±10.1 years). Impulsivity was correlated with both, a more anterior location of the Go- ( r=0.58, P<0.01) and the NoGo-centroid ( r=0.53, P=0.01). These results indicate, that in healthy subjects the amount of I 7 -impulsivity is associated with differences in the prefrontal brain activation pattern during cognitive response control. However, a replication study with a larger sample and an investigation of psychiatric patients with pathological levels of impulsivity are necessary to qualify these topographical ERP-parameters of cognitive response control as valid measures of the brain electrical basis of impulsive behavior.

Auditory and visual event-related potentials in alcoholics: abnormalities of components and brain electrical field.

Alterations of ERPs recorded over midline scalp sites have frequently been reported in alcoholics. To assess the P3 and other ERP components topographically, auditory and visual ERPs were recorded from 33 scalp electrodes in abstinent alcoholics and healthy controls using an oddball paradigm. At the Cz electrode the alcoholics showed decreased visual N1 and increased auditory N2 amplitudes. Topographically, the negative centroids of the visual N1 and P3 and the auditory N2 differed between groups, and the positive centroid of the visual P3 was displaced toward the right hemisphere. While no valid diagnostic classification could be obtained by using the traditional ERP component P3 recorded from Pz, the combination of visual N1 and auditory N2 amplitudes at Cz with centroid parameters amounted to 51% explained variance and 92% correct discrimination of alcoholics from controls. Abnormalities of N1 amplitude and P3 topography similar to the current findings in alcoholics have previously been described for schizophrenics.

Stability of late event-related potentials: topographical descriptors of motor control compared with the P300 amplitude.

The P300-amplitude evoked with an acoustic oddball-paradigm is considered the most stable late event-related potential (ERP). This amplitude-index has become a standard parameter in electrophysiology. Recently, a robust ERP-parameter (NoGo-anteriorization, NGA) has been introduced, which reflects spatial brain electrical changes in relation to execution and inhibition of a motor response elicited with a Continuous Performance Test (CPT). The current study refers to the stability of this new topographical ERP-parameter compared to the stability of the classical P300-amplitude. For that purpose, 12 healthy subjects were investigated with both paradigms during recording of a 21-channel EEG. Analysis of the resulting ERPs revealed a very high stability for both, topographical and amplitude index: In every single subject, the brain electrical fields were characterized by a more anterior location in the NoGo- compared to the Go-condition (=NGA) and by higher amplitudes after target compared to distractor condition. T-tests, analyses of the effect size and of the power revealed equivalent differences between the two contrasting conditions for the topographical compared to the amplitude index. These results indicate that the stability of the topographical ERP-parameters elicited with the CPT is sufficient for an electrophysiological standard-index. The possibility to elicit a robust and specific spatial brain activation with the CPT is an ideal completion to the classical P300 amplitude effect and, therefore, hopefully will be a useful expansion of the standard paradigms in electrophysiological laboratories.

A Study of Brain Electric Field Activity during the Dance Image of Sarupuri

A Study of Brain Electric Field Activity during the Dance Image of Sarupuri

A deviant EEG brain microstate in acute, neuroleptic-naive schizophrenics at rest.

Momentary brain electric field configurations are manifestations of momentary global functional states of the brain. Field configurations tend to persist over some time in the sub-second range ("microstates") and concentrate within few classes of configurations. Accordingly, brain field data can be reduced efficiently into sequences of re-occurring classes of brain microstates, not overlapping in time. Different configurations must have been caused by different active neural ensembles, and thus different microstates assumably implement different functions. The question arises whether the aberrant schizophrenic mentation is associated with specific changes in the repertory of microstates. Continuous sequences of brain electric field maps (multichannel EEG resting data) from 9 neuroleptic-naive, first-episode, acute schizophrenics and from 18 matched controls were analyzed. The map series were assigned to four individual microstate classes; these were tested for differences between groups. One microstate class displayed significantly different field configurations and shorter durations in patients than controls; degree of shortening correlated with severity of paranoid symptomatology. The three other microstate classes showed no group differences related to psychopathology. Schizophrenic thinking apparently is not a continuous bias in brain functions, but consists of intermittent occurrences of inappropriate brain microstates that open access to inadequate processing strategies and context information

Spatio-temporal analysis of electric brain activity during semantic and phonological word processing

There is an ongoing debate in cognitive neuroscience about the time course and the functional independence of the different processes involved in encoding written language material. New data indicate very fast and highly parallel language analysis networks in the brain. Here we demonstrate a methodological approach to study the temporal dynamics of this network by searching for time periods where different task demands emphasize different aspects of the network. Multi-channel event related potentials (ERPs) were recorded during a semantic and a phonological reading task from 14 healthy subjects. Signals were analyzed exclusively on the basis of the spatial configuration of the electric potential distributions (ERP maps), since differences in these spatial patterns directly reflect changes in the configuration of the active sources in the brain. This analysis did not reveal any differences of the evoked brain electric fields between the two tasks up to 280 ms post-stimulus. The ERP maps then differed for a brief period between 280 and 380 ms, before they were similar again. The analysis of the maps using a global linear localization procedure revealed a network of areas, active in both tasks, that mainly involved the left postero-temporal and left antero-temporal regions. The left posterior activation was found already around 100 ms post-stimulus, indicating that language-specific functions appear early in time. We therefore conclude that phonological and semantic processing are essentially performed in both tasks and that only late decision-related processes influence the relative strength of activity of the different modules in the complex language network.

Brain spatial microstates of human spontaneous alpha activity in relaxed wakefulness, drowsiness period, and REM sleep.

Spontaneous alpha activity clearly present in relaxed wakefulness with closed eyes, drowsiness period at sleep onset, and REM sleep was studied with spatial segmentation methods in order to determine if the brain activation state would be modulating the alpha spatial microstates composition and duration. These methods of spatial segmentation show some advantages: i) they extract topographic descriptors independent of the chosen reference (reference-free methods), and ii) they achieve spatial data reduction that are more data-driven than dipole source analysis. The results obtained with this study revealed that alpha activity presented a different spatio-temporal pattern of brain electric fields in each arousal state used in this study. These differences were reflected in a) the mean duration of alpha microstates (longer in relaxed wakefulness than in drowsy period and REM sleep), b) the number of brain microstates contained in one second (drowsiness showed more different microstates than did relaxed wakefulness and REM state), and c) the number of different classes (more abundant in drowsiness than in the rest of brain states). If we assume that longer segments of stable brain activity imply a lesser amount of different information to process (as reflected by a higher stability of the brain generator), whereas shorter segments imply a higher number of brain microstates caused by more different steps of information processing, it is possible that the alpha activity appearing in the sleep onset period could be indexing the hypnagogic imagery self-generated by the sleeping brain, and a phasic event in the case of REM sleep. Probably, REM-alpha bursts are associated with a brain microstate change (such as sleep spindles), as demonstrated by its phasic intrusion in a desynchronized background of brain activity. On the other hand, alpha rhythm could be the "baseline" of brain activity when the sensory inputs are minimum and the state is relaxed wakefulness.

Affective attitudes to face images associated with intracerebral EEG source location before face viewing

We investigated whether different, personality-related affective attitudes are associated with different brain electric field (EEG) sources before any emotional challenge (stimulus exposure). A 27-channel EEG was recorded in 15 subjects during eyes-closed resting. After recording, subjects rated 32 images of human faces for affective appeal. The subjects in the first (i.e., most negative) and fourth (i.e., most positive) quartile of general affective attitude were further analyzed. The EEG data (mean=25±4.8 s/subject) were subjected to frequency-domain model dipole source analysis (FFT-Dipole-Approximation), resulting in 3-dimensional intracerebral source locations and strengths for the delta–theta, alpha, and beta EEG frequency band, and for the full range (1.5–30 Hz) band. Subjects with negative attitude (compared to those with positive attitude) showed the following source locations: more inferior for all frequency bands, more anterior for the delta–theta band, more posterior and more right for the alpha, beta and 1.5–30 Hz bands. One year later, the subjects were asked to rate the face images again. The rating scores for the same face images were highly correlated for all subjects, and original and retest affective mean attitude was highly correlated across subjects. The present results show that subjects with different affective attitudes to face images had different active, cerebral, neural populations in a task-free condition prior to viewing the images. We conclude that the brain functional state which implements affective attitude towards face images as a personality feature exists without elicitors, as a continuously present, dynamic feature of brain functioning.

514 Cardiovascular reactivity, EEG asymmetries and personality traits relations

We investigated whether different, personality-related affective attitudes are associated with different brain electric field (EEG) sources before any emotional challenge (stimulus exposure). A 27-channel EEG was recorded in 15 subjects during eyes-closed resting. After recording, subjects rated 32 images of human faces for affective appeal. The subjects in the first (i.e., most negative) and fourth (i.e., most positive) quartile of general affective attitude were further analyzed. The EEG data (mean=25±4.8 s/subject) were subjected to frequency-domain model dipole source analysis (FFT-Dipole-Approximation), resulting in 3-dimensional intracerebral source locations and strengths for the delta–theta, alpha, and beta EEG frequency band, and for the full range (1.5–30 Hz) band. Subjects with negative attitude (compared to those with positive attitude) showed the following source locations: more inferior for all frequency bands, more anterior for the delta–theta band, more posterior and more right for the alpha, beta and 1.5–30 Hz bands. One year later, the subjects were asked to rate the face images again. The rating scores for the same face images were highly correlated for all subjects, and original and retest affective mean attitude was highly correlated across subjects. The present results show that subjects with different affective attitudes to face images had different active, cerebral, neural populations in a task-free condition prior to viewing the images. We conclude that the brain functional state which implements affective attitude towards face images as a personality feature exists without elicitors, as a continuously present, dynamic feature of brain functioning.

Event-related correlates of response suppression as indicators of novelty seeking in alcoholics.

Novelty Seeking including impulsive behaviour is a personality dimension which has been shown to be related to early-onset alcoholism and to high relapse rates. The cued Continuous Performance Test (CPT) is an experimental paradigm for active response control requiring a choice reaction between execution (Go) and inhibition (NoGo) of a prepared motor response. Metabolic functional methods have shown right frontal brain activation throughout the period of a CPT, and the spatial analysis of the associated event-related brain electrical (ERP) field potentials revealed that this right frontal activation was due to the NoGo subset of the task. The ERP fields allow distinction between the Go and NoGo conditions with one spatial parameter (NoGo-anteriorization) in single cases. and the magnitude of this parameter is thought to be related to inhibitory frontal lobe control. Twenty patients with severe alcohol dependence and 20 age- and sex-matched healthy controls were included in the study and investigated with a 21-channel electroencephalogram while performing a cued CPT. Consistent with previous studies, NoGo-anteriorization was present in every case in both groups. The ERP field differed between alcoholics and controls in the Go condition (P < 0.05) and NoGo-anteriorization in alcoholics was correlated inversely with Novelty Seeking in Cloninger's Temperament and Character Inventory (r= 0.67, P < 0.01). This indicates a reduced frontal lobe contribution during response control in alcoholics with impulsive behaviour and identifies a possible biological marker for the clinical evaluation of the risk of relapse in alcoholism.

Three-dimensional tomography of event-related potentials during response inhibition: evidence for phasic frontal lobe activation

Objectives: Spatial analysis of the evoked brain electrical fields during a cued revealed an extremely robust anteriorization of the positivity of a P300 microstate in the NoGo compared to the Go condition (NoGo-anteriorization in a prevailing study). To allow a neuroanatomical interpretation the NoGo-anteriorization was investigated with a new three-dimensional source tomography method (LORETA) was applied. Methods: The test contains subsets of stimuli requiring the execution (Go) or the inhibition (NoGo) of a cued motor response which can be considered as mutual control conditions for the study of inhibitory brain functions. 21-channel ERPs were obtained from 10 healthy subjects during a cued CPT, And analyzed with LORETA. Results: Topographic analyses revealed significantly different scalp distributions between the Go and the NoGo conditions in both P100 and P300 microstates, indicating that already at an early stage different neural assemblies are activated. LORETA disclosed a significant hyperactivity located in the right frontal lobe during the NoGo condition in the P300 microstate. Conclusions: The results indicate that right frontal sources are responsible for the NoGo-anteriorization of the scalp P300 which is consistent with animal and human lesion studies of inhibitory brain functions. Furthermore, it demonstrates that frontal activation is confined to a brief microstate and time-locked to phasic inhibitory motor control. This adds important functional and chronometric specificity to findings of frontal activation obtained with PET and Near-Infrared-Spectroscopy studies during the cued CPT, and suggests that these metabolic results are not due to general task demands.

Brain electric microstates and momentary conscious mind states as building blocks of spontaneous thinking: I. Visual imagery and abstract thoughts

Prompted reports of recall of spontaneous, conscious experiences were collected in a no-input, no-task, no-response paradigm (30 random prompts to each of 13 healthy volunteers). The mentation reports were classified into visual imagery and abstract thought. Spontaneous 19-channel brain electric activity (EEG) was continuously recorded, viewed as series of momentary spatial distributions (maps) of the brain electric field and segmented into microstates, i.e. into time segments characterized by quasi-stable landscapes of potential distribution maps which showed varying durations in the sub-second range. Microstate segmentation used a data-driven strategy. Different microstates, i.e. different brain electric landscapes must have been generated by activity of different neural assemblies and therefore are hypothesized to constitute different functions. The two types of reported experiences were associated with significantly different microstates (mean duration 121 ms) immediately preceding the prompts; these microstates showed, across subjects, for abstract thought (compared to visual imagery) a shift of the electric gravity center to the left and a clockwise rotation of the field axis. Contrariwise, the microstates 2 s before the prompt did not differ between the two types of experiences. The results support the hypothesis that different microstates of the brain as recognized in its electric field implement different conscious, reportable mind states, i.e. different classes (types) of thoughts (mentations); thus, the microstates might be candidates for the `atoms of thought'.

Faces and emotions: brain electric field sources during covert emotional processing

Covert brain activity related to task-free, spontaneous (i.e. unrequested), emotional evaluation of human face images was analysed in 27-channel averaged event-related potential (ERP) map series recorded from 18 healthy subjects while observing random sequences of face images without further instructions. After recording, subjects self-rated each face image on a scale from “liked” to “disliked”. These ratings were used to dichotomize the face images into the affective evaluation categories of “liked” and “disliked” for each subject and the subjects into the affective attitudes of “philanthropists” and “misanthropists” (depending on their mean rating across images). Event-related map series were averaged for “liked” and “disliked” face images and for “philanthropists” and “misanthropists”. The spatial configuration (landscape) of the electric field maps was assessed numerically by the electric gravity center, a conservative estimate of the mean location of all intracerebral, active, electric sources. Differences in electric gravity center location indicate activity of different neuronal populations. The electric gravity center locations of all event-related maps were averaged over the entire stimulus-on time (450 ms). The mean electric gravity center for disliked faces was located (significant across subjects) more to the right and somewhat more posterior than for liked faces. Similar differences were found between the mean electric gravity centers of misanthropists (more right and posterior) and philanthropists. Our neurophysiological findings are in line with neuropsychological findings, revealing visual emotional processing to depend on affective evaluation category and affective attitude, and extending the conclusions to a paradigm without directed task.