Biomedical subjects

M Martin-Loeches

Publications and source records attributed to M Martin-Loeches.

7 recordsLinked to original sources

PubMed1997

Sources and topography of supramodal effects of spatial attention in ERP.

This study aimed to finding modality-independent event-related potentials (ERP) modulations related to spatial attention by minimising several possible methodological constrains which may account for the rareness of this finding in past spatial attention ERP research. ERP were recorded while subjects performed a shifting spatial attention task of either auditory, visual or mixed (both auditory and visual) modality. Task requirements and stimulation devices were identical for either modality. Stimuli could appear (80%, valid trials) or not (invalid trials) at predicted locations, and subjects had to perform a speeded response to every stimulus. Reaction time benefits were found for valid trials. Instead of the usually found enhancement of sensory-evoked modality-specific components for valid trials, ERP showed modality-independent modulations as a function of attention. They consisted of a fronto-central activity starting 240 ms after stimulus onset and originated in the anterior cingulate gyrus, followed 40 ms later by a bilateral parietal cortex activation. These processes would be reflecting the activity, respectively, of the anterior and posterior attention systems postulated in Posner's model (Posner and Peterson 1990), which showed a higher degree of participation during invalid trials. P300-like processes were also observed for invalid trials. These results demonstrate that supramodal effects of spatial attention of ERP can be obtained. Furthermore, they extend Posner's model by indicating the timings of implication of the attention subsystems.

Acoustic Stimulation↗

PubMed1995

Cerebral perfusion, electrical activity and effects of serotonergic treatment in obsessive-compulsive disorder. A preliminary study.

An abnormally increased glucose metabolism has been described with positron emission tomography (PET) in frontal and caudate regions of obsessive-compulsive patients. Perfusion and electroencephalographic studies have been less conclusive. However, these techniques are, currently, more available than PET and, therefore, deserve further study because of their possible clinical applications. In this article, 13 obsessive-compulsive patients were studied with quantitative EEG and auditory and visual evoked potentials. Six of them were studied also with perfusion single photon emission tomography. A group of 4 patients was studied with both techniques before and after a serotonergic treatment. Increased global, beta, and theta electrical power together with an increased perfusion in frontal regions was observed. The patients also showed a delta power increase over right temporal and frontal regions, together with increased perfusion in the right basal ganglia region as well as a decreased amplitude of the P50 and N100 waves of the auditory evoked potentials over temporal electrodes; these alterations were reduced with treatment. These results are discussed in the context of current data about serotonergic neurotransmission.

Adult↗

PubMed1994

Human brain potentials of spatial location encoding into memory.

Event-related potentials (ERP) were elicited by little vertical bars located randomly in 1 of 4 positions (top, bottom, left or right) relative to a central fixation point. There were 4 experimental conditions requiring the subjects either to press a button if the stimulus was in the target location, count the number of stimuli appearing in the target location, look at the stimuli passively or memorize the location of the stimulus. The interstimulus interval was 2 sec for all tasks. In the memory condition subjects had to consider stimuli as pairs, memorize the location of the first stimulus of every pair and press a button if the second stimulus was in the same location. Our results indicate that ERPs corresponding to the memorization and retention of spatial location are different from those of the other 3 tasks in the presence of a long duration negativity mainly distributed bilaterally over O1, O2, T5 and T6 electrodes. This negativity seems to develop gradually several milliseconds before stimulus onset, reaches its highest value when the spatial location is assumed to be analyzed, and continues with uniform scalp distribution until the end of the recording (822 msec after stimulus onset).

Adolescent↗

PubMed1993

Two-Hz wide EEG bands in Alzheimer's disease.

Twenty Alzheimer's Disease (AD) patients in a mild to moderate stage of the disease and 20 control subjects were compared in 17 2-Hz wide bands from the electrodes 01, 02, P3, P4, T5, T6, F3, F4, F7, F8, Fp1, and Fp2. Differences reached statistical significance for 0-2 and 4-6 Hz bands, where AD patients presented highest power values. The AD group was divided into two groups according to the stage of disease. Both groups of patients presented 0-2 Hz increase in frontal, right parieto-temporal, and occipital areas. The increase in 4-6 Hz band was mainly over frontal areas in both groups and over left parietal region in moderate AD patients. These results and those relative to dominant frequency and crossover frequency between groups are discussed according to previous results with conventional and 2-Hz wide bands in AD patients in a severe stage of the disease.

Aged↗

PubMed1992

Brain mapping in dysphonemic dyslexia: in resting and phonemic discrimination conditions.

Topographic mapping of EEG bands and alpha asymmetry were analyzed during resting conditions and an auditory phonemic discrimination task (APD) in carefully screened samples of 9.0- to 12-year-old control and dysphonemic-sequencing dyslexic children. The EEG was recorded over the entire scalp, with a linked ears reference. We found: (1) no differences between groups during resting conditions in any frequency band analyzed; (2) a left hemisphere alpha responsiveness in dyslexic children during the APD condition; and (3) a beta 2 decrease in the left posterior quadrant in dyslexics during the APD condition. We conclude that the lower alpha and beta 2 responsiveness may be due to a diminished cortical reactivity and may be related to intrinsic disorganization of the neural processors associated directly with the APD task demands, the alpha activity reflecting poor attention to an external stimuli source and the beta 2 decrease reflecting an unusual processing associated with the linguistic cognitive requirements.

Auditory Perception↗

PubMed1991

Topography of mobility and complexity parameters of the EEG in Alzheimer's disease.

Mobility and complexity, Hjorth's parameters of the electroencephalogram (EEG), were calculated in 16 electrodes in a group of 14 patients with probable Alzheimer's disease (AD) and 14 healthy controls. Mobility was decreased in the AD group, differences reaching high levels of significance over all the electrodes. Complexity was increased significantly in the AD group only in five electrodes. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for mobility at each electrode, considering only those AD patients with the lowest cognitive impairment. Sensitivity and negative predictive value were 100% at all the electrodes. Specificity and positive predictive value at several electrodes reached highly acceptable proportions, such as 71% or more for the former, and 64% or more for the latter. Implications of mobility in the early diagnosis of AD are discussed.

Aged↗

PubMed1991

Topographic maps of brain electrical activity in primary degenerative dementia of the Alzheimer type and multiinfarct dementia.

The topography of the electroencephalographic (EEG) pattern of ten patients with primary degenerative dementia of the Alzheimer type, ten multiinfarct dementia patients, and ten age-matched controls was compared during three different behavioral conditions: resting condition with eyes open (EO), memorizing a list of words (M), and recalling the same list of words (R). Results indicate that the alpha frequency band does not show significant changes. On the other hand, the theta band could be considered an important factor in the differential diagnosis of the primary degenerative dementia of the Alzheimer type, showing a higher power over right posterior regions in this group of patients compared with the multiinfarct dementia patients under different behavioral conditions.

Aged↗