Low-resolution Electromagnetic Tomography Analysis Research Articles

The electrophysiological “delayed effect” of focal interictal epileptiform discharges. A low resolution electromagnetic tomography (LORETA) study

Collating the findings regarding the role of focal interictal epileptiform discharges (IEDs) on CNS functions raises the possibility that IEDs might have negative impact that outlasts the duration of the spike-and-wave complexes. The aim of this study was the electrophysiological demonstration of the "delayed effect" of the IEDs. 19-channel, linked-ears referenced, digital waking EEG records of 11 children (aged 6-14 years, eight with idiopathic, three with cryptogenic focal epilepsy, showing a single spike focus) were retrospectively selected from our database. A minimum of 20 (preferably, 30), 2-s epochs containing a single focal spike-and-wave complex were selected (Spike epochs). Thereafter, Postspike-1 (Ps1), Postspike-2 (Ps2) and Postspike-3 (Ps3) epochs were selected, representing the first and second seconds (Ps1), the third and fourth seconds (Ps2) and the fifth and sixth seconds (Ps3) after the Spike epoch, respectively. Interspike epochs (Is) were selected at a distance at least 10s after the Spike epoch. Individual analysis: the frequency of interest (FOI=the individual frequency of the wave component of the IEDs), and the region of interest (ROI=the site of the IEDs) were identified by reading the raw EEG waveform and the instant power spectrum. Very narrow band LORETA (low resolution electromagnetic tomography) analysis at the FOI and ROI was carried out. Age-adjusted, Z-transformed LORETA "activity" (=current source density, amperes/meters squared) was compared in the Spike, Ps1, Ps2, Ps3 and Is epochs. the greatest (uppermost pathological) Z-scores and the greatest spatial extension of the LORETA-abnormality were always found in the Spike epochs, followed by the gradual decrease of activity in terms of severity and spatial extension in the Ps1, Ps2, Ps3 epochs. The lowest (baseline) level and extension of the abnormality was found in the Is epochs. Group analysis: average values of activity across the patients were computed for the temporal decrease of the abnormality. a clear tendency for the decrease of abnormality was demonstrated. the "delayed effect" of the IEDs was demonstrated electrophysiologically and quantified. The method may be utilized in the individual assessment of the effect of IEDs on cortical activity, the degree and temporo-spatial extension of the abnormality.

Antipsychotic effect of electroconvulsive therapy is related to normalization of subgenual cingulate theta activity in psychotic depression

Objective Electroconvulsive therapy (ECT) is one of the most effective options available for treating depressive and psychotic symptoms in a variety of disorders. While the exact mechanism of ECT is unclear, it is known to increase metabolism and blood flow specifically in the anterior cingulate cortex (ACC). The ACC is a cortical generator of theta rhythms, which are abnormal in patients with depression and psychotic disorders. Since patients with psychotic depression are known to respond particularly robustly to ECT, we investigated whether the therapeutic effect of ECT in this population was related to normalization of abnormal theta activity in the ACC. Method We obtained 19-lead electroencephalography (EEG) data from 17 participants with psychotic depression before and 2–3 weeks after a full course of ECT. EEG data was analyzed with quantitative measures and low-resolution electromagnetic tomography (LORETA) compared to an age-adjusted normative database. Results Quantitative EEG analyses revealed that theta band (4–7 Hz) activity was the only frequency band that changed with ECT. LORETA analyses revealed that the primary site of theta activity change was within the subgenual ACC (Brodmann area 25). There was a positive association between increased subgenual ACC theta activity and decreased psychotic symptoms. The degree of low theta activity in the subgenual ACC prior to ECT predicted the antipsychotic response of ECT. Conclusions The antipsychotic effect of ECT is related to normalization of subgenual ACC theta hypoactivity.

EEG Correlates of Action Observation in Humans

To investigate electrophysiological correlates of action observation electroencephalogram (EEG) was recorded while participants observed repetitive biological (human) or non-biological movements (at a rate of 2 Hz). Steady-state evoked potentials were analyzed and their neural sources were investigated using low resolution electromagnetic tomography analysis (LORETA). Results revealed significantly higher activation in the primary motor and premotor cortex, supplementary motor area as well as the posterior parietal cortices during observation of biological movements, supporting mirror properties of cortical motor neurons. In addition interregional communication was analyzed. Increased coherence for distributed networks at delta (0.5-4 Hz) and lower alpha (8-10 Hz) frequencies were obtained suggesting integration and functional coupling between the activated cortical regions during human action observation.

Pseudohomophone effects provide evidence of early lexico‐phonological processing in visual word recognition

Previous research using event-related brain potentials (ERPs) suggested that phonological processing in visual word recognition occurs rather late, typically after semantic or syntactic processing. Here, we show that phonological activation in visual word recognition can be observed much earlier. Using a lexical decision task, we show that ERPs to pseudohomophones (PsHs) (e.g., ROZE) differed from well-matched spelling controls (e.g., ROFE) as early as 150 ms (P150) after stimulus onset. The PsH effect occurred as early as the word frequency effect suggesting that phonological activation occurs early enough to influence lexical access. Low-resolution electromagnetic tomography analysis (LORETA) revealed that left temporoparietal and right frontotemporal areas are the likely brain regions associated with the processing of phonological information at the lexical level. Altogether, the results show that phonological processes are activated early in visual word recognition and play an important role in lexical access.

Imaging the cortical effect of lamotrigine in patients with idiopathic generalized epilepsy: A low-resolution electromagnetic tomography (LORETA) study

Anatomical localization of the cortical effect of lamotrigine (LTG) in patients with idiopathic generalized epilepsy (IGE). 19 patients with untreated IGE were investigated. EEG was recorded in the untreated condition and 3 months later when LTG treatment abolished the seizures. 19-channel EEG was recorded, and a total of 2min artifact-free, waking EEG was processed to low-resolution electromagnetic tomography (LORETA) analysis. Activity (that is, current source density, A/m(2)) was computed in four frequency bands (delta, theta, alpha, and beta), for 2394 voxels that represented the cortical gray matter and the hippocampi. Group differences between the untreated and treated conditions were computed for the four bands and all voxels by multiple t-tests for interdependent datasets. The results were presented in terms of anatomical distribution and statistical significance. p<0.01 (uncorrected) changes (decrease of activity) emerged in the theta and the alpha bands. Theta activity decreased in a large cluster of voxels including parts of the temporal, parietal, occipital cortex bilaterally, and in the transverse temporal gyri, insula, hippocampus, and uncus on the right side. Alpha activity decreased in a relatively smaller cortical area involving the right temporo-parietal junction and surrounding parts of the cortex, and part of the insula on the right side. LTG decreased theta activity in several cortical areas where abnormally increased theta activity had been found in a prior study in another cohort of untreated IGE patients [Clemens, B., Bessenyei, M., Piros, P., Tóth, M., Seress, L., Kondákor, I., 2007b. Characteristic distribution of interictal brain electrical activity in idiopathic generalized epilepsy. Epilepsia 48, 941-949]. These LTG-related changes might be related to the decrease of seizure propensity in IGE.

Spatiotemporal dynamics of single-letter reading: a combined ERP-FMRI study.

This work investigates the neural correlates of single-letter reading by combining event-related potentials (ERPs) and functional magnetic resonance imaging (fMRI), thus exploiting their complementary spatiotemporal resolutions. Three externally-paced reading tasks were administered with an event-related design: passive observation of letters and symbols and active reading aloud of letters. ERP and fMRI data were separately recorded from 8 healthy adults during the same experimental conditions. Due to the presence of artifacts in the EEG signals, two subjects were discarded from further analysis. Independent Component Analysis was applied to ERPs, after dimensionality reduction by Principal Component Analysis: some independent components were clearly related to specific reading functions and the associated current density distributions in the brain were estimated with Low Resolution Electromagnetic Tomography Analysis method (LORETA). The impulse hemodynamic response function was modeled as a linear combination of linear B-spline functions and fMRI statistical analysis was performed by multiple linear regression. fMRI and LORETA maps were superimposed in order to identify the overlapping activations and the activated regions specifically revealed by each modality. The results showed the existence of neuronal networks functionally specific for letter processing and for explicit verbal-motor articulation, including the temporo-parietal and frontal regions. Overlap between fMRI and LORETA results was observed in the inferior temporal-middle occipital gyrus, suggesting that this area has a crucial and multifunctional role for linguistic and reading processes, likely because its spatial location and strong interconnection with the main visual and auditory sensory systems may have favored its specialization in grapheme-phoneme matching.

Electrophysiological basis for the ability of olanzapine to improve verbal memory and functional outcome in patients with schizophrenia: A LORETA analysis of P300

Abnormality of P300 waveforms of event-related potentials (ERPs) has been suggested to represent an aspect of the pathophysiology of schizophrenia. Previous work points to the contribution of altered neural function in discrete brain regions in the left hemisphere to psychotic symptoms and cognitive deficits of schizophrenia. In this study, we sought to determine: 1) if patients with schizophrenia elicit a decreased P300 current source density in brain areas, such as the superior temporal gyrus (STG); 2) if decreased P300 generator density in the left STG is recovered by treatment with the most widely-used antipsychotic drug olanzapine; and 3) if the recovery of P300 source density is associated with improvements of cognitive and functional status. P300 in response to an auditory oddball task, as well as verbal learning memory, psychopathology, and quality of life were evaluated in 16 right-handed patients with schizophrenia before and after treatment with olanzapine for 6 months. ERP data were also obtained from 16 right-handed age and gender-matched normal volunteers. Low resolution electromagnetic tomography (LORETA) analysis was used to obtain current density images of P300. Patients with schizophrenia showed significantly smaller LORETA values in several brain regions in the left side, particularly STG, middle frontal gyrus, and precentral gyrus, compared with control subjects. Six-month treatment with olanzapine significantly increased P300 source density only in the left STG. Positive symptoms, negative symptoms, verbal learning memory, and quality of life were also improved during treatment. Significant correlations were found between the increase in LORETA values of left STG vs. improvements of negative symptoms, as measured by Scale for the Assessment of the Negative Symptoms, and verbal learning memory, as measured by the Japanese Verbal Learning Test. Improvement of quality of life, as evaluated by the Quality of Life Scale, were significantly associated with an increase in LORETA values of middle frontal gyrus, and tended to correlate with that of precentral gyrus. The results of this study suggest that changes in cortical activity, as measured by ERPs, are responsible for the ability of some antipsychotic drugs to improve cognition and functional outcome in patients with schizophrenia.

Comparison of Low Resolution Electromagnetic Tomography Imaging Between Subjects With Mild and Severe Obstructive Sleep Apnea Syndrome: A Preliminary Study

ObjectiveThe purpose of this study was to identify the regions of the brain associated with recurrent nocturnal chronic hypoxic episodes in patients with untreated obstructive sleep apnea syndrome (OSAS) using low-resolution electromagnetic tomography (LORETA) and quantitative electroencephalography (QEEG).MethodsNocturnal polysomnograph (NPSG) and subsequent morning electroencephalograph (EEG) were measured in 20 subjects with OSAS. Mild (n=10 ages 39.5±12.1 years) and severe (n=10 ages 41.7±13.6 years) right-handed male OSAS subjects were selected by interview and questionnaires including the NPSG, Beck Depression Inventory, Beck Anxiety Inventory, Epworth Sleepiness Scale, and Pittsburgh Sleep Quality Index. The LORETA and QEEG were compared between the severe and mild OSAS groups by frequency bands (delta 1-3 Hz, theta 4-7 Hz, alpha 8-12 Hz, beta1 13-18 Hz, beta2 19-21 Hz, beta3 22-30 Hz, and total 1-30 Hz) made by spectral analysis during resting with the eyes closed.ResultsThe LORETA analysis showed decreased alpha activity at the right posterior cingulate gyrus (Brodmann area 23) in cases with severe OSAS compared to mild OSAS (p<0.05). For the QEEG, the absolute power of the alpha activity (8-12 Hz) was decreased in P3 (p=0.047), PZ (p=0.039) and O2 (p=0.04) in cases with severe OSAS compared to mild OSAS cases. The LORETA and QEEG analyses had similar results with regard to band, activation and location.ConclusionThe decreased activity of the alpha frequency in the right posterior cingulate gyrus, in patients with severe OSAS compared to those with mild OSAS, suggests that chronic repeated short-term hypoxia during sleep, in OSAS, could provoke cortical brain dysfunction associated with cognitive dysfunction such as memory and attention.

Dissociation of sustained attention from central executive functions: local activity and interregional connectivity in the theta range

Human brain oscillatory activity was analysed in the electroencephalographic theta frequency range (4-7 Hz) while subjects executed complex sequential finger movements with varying task difficulty and memory load. Local frontal-midline theta activity was associated with the general level of cognitive demand, with the highest amplitudes in the most demanding condition. Using low-resolution electromagnetic tomography analysis (LORETA), this theta activity was localized in the anterior cingulate gyrus including the cingulate motor area. These results suggest that local theta activity in the anterior cingulate gyrus represents correlates of an attentional system that allocate cognitive resources. In addition, interregional connectivity in the theta frequency range was modulated by memory-related executive functions independently of task difficulty. Connectivity analyses revealed a more distributed long-range network including frontal and parietal cortices during execution of novel compared with well-trained finger movement sequences. Thus, these results are compatible with a model in which theta long-range coupling indicates integration of sensory information into executive control components of complex motor behaviour.

Gamma oscillatory activity in a visual discrimination task

We tested the hypothesis whether images of real objects elicit stronger gamma (>25 Hz) synchronization, when compared with scrambled objects. The background of this study is a recent debate about the functional meaning of evoked and induced gamma oscillations. Brain electrical source analysis (BESA) and low resolution electromagnetic tomography analysis (LORETA) was performed on the basis of the event-related potential (ERP) data. A component at around 230 ms (termed C230) showed strongest differences between objects and scrambled objects. Time–frequency analyses were run across electrodes and within the dipole sources. We found increased gamma event-related synchronization (ERS) between 200 and 300 ms for real objects. This effect was strongest in a fronto-medial source. Induced gamma, as also shown in previous studies, reflects the more task-relevant mechanism where object representations become activated.

An orienting reflex perspective on anteriorisation of the P3 of the event-related potential

In the Go/NoGo task, the P3 component of the event-related potential elicited by NoGo stimuli is topographically anterior to that from Go stimuli. This anteriorisation has been linked to the response inhibition thought to be required when NoGo stimuli are presented, and suggested as an index of inhibition. We report a preliminary investigation of this question from an orienting reflex (OR) perspective, in which the autonomic skin conductance response (SCR) was used as an OR "yardstick". We presented subjects with a random mix of 15 target and 15 non-target auditory stimuli with a short inter-stimulus interval, and explored the sources of the resultant P3s using low-resolution electromagnetic tomography (LORETA). Across-subject mean SCRs showed exponential decrement over trials and a larger response to targets, as expected from the OR perspective. LORETA analysis of the across-subject mean initial P3s showed exponential response decrement of their common sources, suggestive of the Novelty P3. Grand mean P3s to targets and non-targets appeared to correspond to the P3b and P3a, respectively. These results suggest that anteriorisation of the P3 to NoGo stimuli may reflect processing related to the basic involuntary OR to indifferent (non-significant) stimuli rather than an active inhibitory process.

Individual differences in brain activity during visuo-spatial processing assessed by slow cortical potentials and LORETA

Using slow-cortical potentials (SCPs), Vitouch et al. (International Journal of Psychophysiology 27 (1997) 183–199) demonstrated that subjects with low ability to solve a complex visuo-spatial imagery task show higher activity in occipital, parietal and frontal cortex during task processing than subjects with high ability. This finding has been interpreted in the sense of the so-called “neural efficiency” hypothesis, which assumes that the central nervous system of individuals with higher intellectual abilities is functioning in a more efficient way than the one of individuals with lower abilities. Using a higher spatial resolution of SCP recordings, and by employing the source localization method of LORETA (low-resolution electromagnetic tomography), we investigated this hypothesis by performing an extended replication of Vitouch et al.'s study. SCPs during processing of a visuo-spatial imagery task were recorded in pre-selected subjects with either high or low abilities in solving the imagery task. Topographic and LORETA analyses of SCPs revealed that a distributed network of extrastriate occipital, superior parietal, temporal, medial frontal and prefrontal areas was active during task solving. This network is well in line with former studies of the functional neuroanatomy of visuo-spatial imagery. Contrary to our expectations, however, the results of Vitouch et al. as well as of other studies supporting the neural efficiency hypothesis could not be confirmed since no difference in brain activity between groups was observed. This inconsistency between studies might be due to differing task processing strategies. While subjects with high abilities in the Vitouch et al. study seemed to use a visuo-perceptual task solving approach, all other subjects relied upon a visuo-motor task processing strategy.

Source localization of mesial temporal interictal epileptiform discharges: Correlation with intracranial foramen ovale electrode recordings

Objective We have investigated the localization accuracy of low-resolution electromagnetic tomography (LORETA) for mesial temporal interictal epileptiform discharges (IED) on a statistical basis by using clinical electroencephalographic (EEG) data of simultaneous scalp and intracranial foramen ovale (FO) electrode recordings. Methods We retrospectively analyzed the IED of 15 patients who underwent presurgical assessment for intractable temporal lobe epilepsy. All patients have subsequently undergone amygdalohippocampectomy. The scalp signals were averaged time-locked to the peak activity in bilateral 10-contact FO electrode recordings. Source modeling was carried out by using statistical non-parametric mapping (SNPM) of LORETA values and by calculating raw LORETA values of averaged IED. The results were compared to intracranial data obtained from FO electrode recordings. Results Two thousand six hundred and fifteen discharges could be attributed to 19 different patterns of intracranial mesial temporal IED. SNPM of LORETA revealed confined ipsilateral mesial temporal solutions for 14 (73.7%) and no significant solutions for five (26.3%) of these patterns. Raw LORETA current density distributions of the 19 averaged IED patterns revealed ipsilateral basal to lateral temporal solutions for the 14 IED patterns with a sufficient signal to noise ratio (SNR), but spurious results for those five IED with a low SNR. Conclusions SNPM of LORETA but not LORETA analysis of averaged IED patterns accurately localizes the source generators of mesial temporal IEDs. Significance SNPM of raw LORETA values might be appropriate for localizing restricted mesial temporal lobe sources.

The neurophysiological time pattern of illusionary visual perceptual transitions: a simultaneous EEG and fMRI study

Several divergent cortical mechanisms generating multistability in visual perception have been suggested. Here, we investigated the neurophysiologic time pattern of multistable perceptual changes by means of a simultaneous recording with electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Volunteers responded to the subjective perception of a sudden change between stable patterns of illusionary motion (multistable transition) during a stroboscopic paradigm. We found a global deceleration of the EEG frequency prior to a transition and an occipital-accentuated acceleration after a transition, as obtained by low-resolution electromagnetic tomography analysis (LORETA) analysis. A decrease in BOLD response was found in the prefrontal cortex before, and an increase after the transitions was observed in the right anterior insula, the MT/V5 regions and the SMA. The thalamus and left superior temporal gyrus showed a pattern of decrease before and increase after transitions. No such temporal course was found in the control condition. The multimodal approach of data acquisition allows us to argue that the top-down control of illusionary visual perception depends on selective attention, and that a diminution of vigilance reduces selective attention. These are necessary conditions to allow for the occurrence of a perception discontinuity in absence of a physical change of the stimulus.

Brain activity of regular and dyslexic readers while reading Hebrew as compared to English sentences

The aim of the present study was to examine differences among ‘regular’ and dyslexic adult bilingual readers when processing reading and reading related skills in their first (L1 Hebrew) and second (L2 English) languages. Brain activity during reading Hebrew and English unexpected sentence endings was also studied. Behavioral and electrophysiological measures including event-related potentials (ERP) and low resolution electromagnetic tomography (LORETA) methodology were employed. Results indicated discrepancies in the processing profiles of dyslexic and regular bilingual readers in both first and second languages. In general, the amplitudes of the evoked potentials were higher and the latencies longer among dyslexic readers during processing of information in first and second languages (L1 and L2), but were more pronounced in English (L2). LORETA analysis indicated evidence that the source of brain activity measured by current density of brain activation is different when reading Hebrew as compared to English sentences mainly among dyslexics and not among regular readers. The data from the present study supports the ‘dominanat bilingual’ hypothesis for defining bilinguals. A discrepancy between achievement in performing various L1 and L2 tasks was consistent across groups. Both groups were better in there mother tongue, which was Hebrew as compared to English.

LORETA analysis of CNV in time perception

The aim of this study was to specify when and where “pure” temporal processing occurred in the brain. Event-related potentials were recorded from 13 young, healthy volunteers performing interval and pitch discrimination tasks. In the interval task, two 1000-Hz tones (S1 and S2) were presented with an interval of 1000 or 1500 ms. Participants were asked to judge whether the S1–S2 interval was short or long. In the pitch task, the S1 (1000 Hz) was followed by the S2 (1000 or 1050 Hz) with a fixed interval of 1000 ms. Participants were asked to judge whether the pitch of the S2 was the same as or different from that of the S1. In both tasks, contingent negative variation (CNV) was observed in the period between 500 and 1000 ms after the S1. The amplitude of the CNV was larger in the interval task than in the pitch task. The data were analyzed using low-resolution electromagnetic tomography (LORETA). The right dorsolateral prefrontal cortex (DLPFC) showed more activation in the interval task than in the pitch task. This result suggests that the right DLPFC may play an important role in time perception and processing the temporal dimension of events.

Abnormalities of P300 cortical current density in unmedicated depressed patients revealed by LORETA analysis of event-related potentials.

The purpose of the present study was to investigate the neural substrates underlying event-related potential (ERP) abnormalities, with respect to the generators of the ERP components in depressed patients. Using an oddball paradigm, ERP from auditory stimuli were recorded from 22 unmedicated patients with current depressive episodes and compared with those from 22 age- and gender-matched normal controls. Cortical current densities of the N100 and P300 components were analyzed using low-resolution electromagnetic tomography (LORETA). Group differences in cortical current density were mapped on a 3-D cortex model. The results revealed that N100 cortical current densities did not differ between the two groups, while P300 cortical current densities were significantly lower in depressed patients over the bilateral temporal lobes, the left frontal region, and the right temporal-parietal area. Furthermore, the cortical area in which the group difference in P300 current density had been identified was remarkably larger over the right than the left hemisphere, thus supporting the hypothesis of right hemisphere dysfunction in depression.

Brain electrical dysfunction of the anterior cingulate in schizophrenic patients

The anterior cingulate cortex (ACC) is a key region within the human prefrontal cortex that has been shown to be dysfunctional in schizophrenic patients. Supporting evidence for this notion has been collected with neuroimaging methods during various cognitive activation tasks. Recently, electrophysiological ACC activity has been demonstrated by means of a three-dimensional source location with low resolution electromagnetic tomography (LORETA) in the event-related potentials elicited during the NoGo condition of the Continuous Performance Test (CPT) as compared to its Go condition. Thirty-one schizophrenic patients and 31 age- and gender-matched healthy volunteers were investigated with this newly developed electrophysiological method. LORETA analysis revealed a significantly diminished brain electrical activity in the ACC of schizophrenic patients as compared to controls during the NoGo condition of the CPT. This result supports the assumption of a functional deficit of the ACC during this cognitive task as a central feature in schizophrenias and, thereby, specifies the general concept of hypofrontality. Moreover, this investigation underscores the value of sophisticated electrophysiological methods in combination with unambiguously designed mental tasks for the evaluation of the pathophysiological processes underlying schizophrenic diseases.

The electrophysiological net response ('F-complex') to spatial fusion of speech elements forming an auditory object.

The purpose of this study was to define and analyze the brain activity associated with fusion of speech elements to form an auditory object and to study the effects of presenting the elements at different spatial locations (duplex stimulus). Stimuli were formant transitions (presented to the front, left or right of the subject) and base (presented to the front), that fused to result in V-C-V sequences /aga/ and /ada/. Ten right-handed, adult, native Hebrew speakers discriminated each fused stimulus, and the brain potentials associated with performance of the task were recorded from 21 electrodes. The net-fusion response, the 'F(fusion)-complex', was extracted by subtracting the sum of potentials to the base and formant transitions from the potentials to the fused sound. Low resolution electromagnetic tomography analysis (LORETA) was performed to assess the timing and brain location of the fusion process. The 'F-complex', comprising of the difference N(1), P(2), N(2b) (FN(1), FP(2), FN(2b)) components could be identified for each of the stimuli and reflected a process indicating inhibition, occlusion or both, with right ear advantage in fusion. LORETA analyses indicate sequential processing of speech fusion in the temporal lobes, beginning with right prominence in FN(1) and FP(2) shifting to a more symmetrical pattern in FN(2). The electrophysiological correlates of speech fusion highlight the uniqueness of speech perception and the brain areas involved in its analysis.

Reduced brain electric activities of frontal lobe in cortical cerebellar atrophy.

To assess the relationship between cerebellum and brain cortical activity without motor factors, we recorded the mid-latency auditory evoked responses (MLRs) with simultaneous recording of the electroencephalography (EEG) at rest in patients with 'pure cortical cerebellar atrophy (CCA)'. We studied 12 normal control subjects and non-demented 'pure CCA' patients determined by quantitative magnetic resonance imaging analysis. A comprehensive neuropsychological test battery assessed intelligence, frontal lobe function and word fluency. Spontaneous eyes-closed resting EEG and MLRs were recorded from 20 scalp electrodes and analysed with low-resolution electromagnetic tomography (LORETA) to compute the 3-dimensional intracerebral distribution of electric activity. Neuropsychological tests revealed no differences between CCA and the control. Analysis of EEG and MLRs using classical methods also did not reveal any differences. LORETA analysis indicated significant decrease of alpha2 activity in the left inferior frontal gyrus in CCA. On MLRs, the most significant difference was observed at P1 component, and CCA patients showed significant decrease at the right superior frontal gyrus. Our results indicated that the frontal lobe and ascending reticular activating system are inhibited in CCA patients, and suggested the involvement of the cerebellum in cortical electric activities irrespective of motor adjunct. Quantitative EEG and MLR measurements with LORETA pointed out frontal lobe hypoactivities in pure CCA patients.