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M Martín-Loeches

Publications and source records attributed to M Martín-Loeches.

At least 19 recordsLinked to original sources
PubMed2001

Emotion and attention interaction studied through event-related potentials.

Several studies on hemodynamic brain activity indicate that emotional visual stimuli elicit greater activation than neutral stimuli in attention-related areas such as the anterior cingulate cortex (ACC) and the visual association cortex (VAC). In order to explore the temporo-spatial characteristics of the interaction between attention and emotion, two processes characterized by involving short and rapid phases, event-related potentials (ERPs) were measured in 29 subjects using a 60-electrode array and the LORETA source localization software. A cue/target paradigm was employed in order to investigate both expectancy-related and input processing-related attention. Four categories of stimuli were presented to subjects: positive arousing, negative arousing, relaxing, and neutral. Three attention-related components were finally analyzed: N280pre (from pretarget ERPs), P200post and P340post (both from posttarget ERPs). N280pre had a prefrontal focus (ACC and/or medial prefrontal cortex) and presented significantly lower amplitudes in response to cues announcing negative targets. This result suggests a greater capacity of nonaversive stimuli to generate expectancy-related attention. P200post and P340post were both elicited in the VAC, and showed their highest amplitudes in response to negative- and to positive-arousing stimuli, respectively. The origin of P200post appears to be located dorsally with respect to the clear ventral-stream origin of P340post. The conjunction of temporal and spatial characteristics of P200post and P340post leads to the deduction that input processing-related attention associated with emotional visual stimulation involves an initial, rapid, and brief "early" attentional response oriented to rapid motor action, being more prominent towards negative stimulation. This is followed by a slower but longer "late" attentional response oriented to deeper processing, elicited to a greater extent by appetitive stimulation.

Adult↗
PubMed2001

P300 amplitude as a possible correlate of frontal degeneration in schizophrenia.

The existence of neurodegeneration is a debated issue in schizophrenia research. The P300 component of event-related electrical potentials (ERP) has been related to the different degree of damage to gray and white matter. This study explores the possible relationship between P300 amplitude and/or latency and the existence of degenerative processes in schizophrenia, by assessing its correlation with volume of sulcal CSF and duration of illness, as transversal indicators of neurodegeneration. Nineteen patients (14 males, 5 females) and 13 controls (6 males, 7 females) were studied with MRI and electrophysiological records (P300). The possible influence of sex and age at the time of the exploration was statistically controlled in both groups. The results show a significant negative correlation between P300 amplitude and prefrontal CSF volume in the patient group. A lower though still significant correlation was also found between P300 amplitude and duration of illness, whereas no correlation was found in the control group. These results support the hypothesis that P300 amplitude may be interpreted as a marker of neurodegeneration in schizophrenia.

Adolescent↗
PubMed2001

Functional differences in the semantic processing of concrete and abstract words.

There is considerable debate as to whether the semantic system is a unitary one in which meanings are available in a peculiar, perceptual-free format, or whether it is functionally segregated into anatomically discrete, modality-specific but semantic regions. In the former case, concrete and abstract words should not differ in the amount of activation of semantic areas. Neuroimaging studies in this field are, however, far from conclusive, and one reason for this may be that the degree of imageability of the stimuli - probably a crucial variable - has not been considered. Recognition Potential (RP) reflects semantic processing and appears to originate in basal extrastriate regions involved in semantic processing. In this study, we compared the RP of concrete and abstract words that actually differ in their degree of imageability. Results indicate that the semantic processing areas in which the RP originates display a higher activation for concrete (more imageable) material, but that abstract material also evokes a notably larger RP component compared with pseudowords or unpronounceable letter strings. Accordingly, the study appears to suggest that there is no full functional segregation of the semantic systems. Rather, our data support the existence of a semantic system that is specialised in concrete, imageable material, and that is also activated, though to a lower extent, by abstract material.

Adolescent↗
PubMed2001

Semantic processing of open- and closed-class words: an event-related potentials study.

Previous research on open- and closed-class words has revealed the existence of several differences in the processing of these types of vocabulary. In this paper the processing of open- and closed-class words was compared by means of an early electrical brain response, recognition potential (RP), which indexes semantic processing and originates from basal extrastriate areas. The effects of word frequency on closed-class words were also investigated. For these purposes, open- and closed-class words, among other stimuli, were presented by means of the rapid stream stimulation procedure. Results showed that there were no significant differences when comparing the RP evoked by open- and closed-class words in the left hemisphere. However, in the right hemisphere this situation changed: the RP evoked by open- and closed-class words did differ. Moreover, there were no differences between the RP evoked by closed-class words and pseudowords. These patterns of results suggest that the semantic processing of closed-class words shares some aspects with the processing of open-class words, despite the existence of some differences. Thus, whereas the semantic processing of open-class words recruits brain areas of both hemispheres, the semantic processing of closed-class words is left-lateralized. A second purpose of this work is to study word-frequency effects on closed-class words. Our results show the insensitivity of closed-class words to word-frequency effects.

Adult↗
PubMed2001

Electrophysiological evidence of a semantic system commonly accessed by animals and tools categories.

Some theoretical perspectives propose a semantic system in which categories are represented in different brain regions. Others assume that distinctions are based rather on differences in the demands placed by different categories on shared processing systems. In this study semantic categorization processes were investigated using the recognition potential (RP), an event-related brain response that reflects semantic processing, peaks at around 250 ms after stimulus onset and originates in areas subserving perceptual-semantic analyses. Results indicate that the RP shows some degree of sensitivity to categorization processes, but that categories assumed to differ markedly in their processing demands share, to a large extent, a common neural generator. This provides support for the non-categorical view on the organization of the semantic system, though introducing subtle variations, and suggesting the existence of a semantic subsystem specializing in the processing of perceptual-semantic features regardless of the semantic category involved.

Adolescent↗
PubMed2001

Studying semantics in the brain: the rapid stream stimulation paradigm.

Event-related potentials (ERPs) provide information about the temporal course of cognitive processes in the brain. They have proved to be a valuable tool in order to explore semantic aspects of word processing. However, to date, research in this field has been mostly concerned with the study of post-lexical features by means of the N400-paradigm. We introduce here the rapid stream stimulation paradigm, in which stimuli reflecting different levels of linguistic information are presented to subjects at a high rate of stimulation. The present protocol shows in detail how this paradigm can be applied. The application of the rapid stream stimulation paradigm evokes the recognition potential (RP), an ERP component that peaks at around 260 ms after stimuli onset and seems to be reflecting lexical selection processes. Results of studies that revealed the sensibility of the RP to visual-semantic aspects and the location of its neural generators within basal extrastriate areas are reported. Although some research has been conducted with the rapid stream stimulation paradigm much remains still to be done. Some of the possibilities that this paradigm offers are further discussed.

Brain↗
PubMed2001

Electrophysiology and intelligence: the electrophysiology of intellectual functions in intellectual disability.

The electroencephalograms (EEGs) of 127 subjects with intellectual disability were analysed with regarding to their correlation to intellectual functions in order to further understand the relationships between EEG and intelligence. The EEG frequency spectrum was subdivided into 15, 2-Hz-wide bands and was recorded from electrodes F1, Fpz, Fp2, F7, F3, Fz, F4, F8, T3, C3, Cz, C4, T4, T5, P3, Pz, P4, T6, O1, Oz and O2. Patterns of acorrelation showed several similarities when compared to other analogous studies with normal subjects. However, the typical finding in the present study was a high number of correlations involving the frontal lobes, mainly the prefrontal portions, which is at variance with the patterns of normal subjects. Frontal lobes, especially the prefrontal regions, seem to be affected, regardless of its aetiology, in subjects with intellectual disability.

Adolescent↗
PubMed2001

An early electrophysiological sign of semantic processing in basal extrastriate areas.

Recognition potential (RP), a recently discovered electrophysiological response of the brain, is sensitive to semantic aspects of stimuli. Given its peak values (about 250 ms), RP may be a good candidate for the study of semantic processing during its occurrence. However, its topography and neural generators are largely unknown. To improve this state of affairs, high-resolution electroencephalography and brain electrical source analysis were carried out. Results suggest a possible origin of RP in the lingual gyrus, hence reflecting the activity of the basal extrastriate areas. RP therefore appears to be a highly valuable tool in the study of those regions considered to be the "third language areas" (in addition to Broca's and Wernicke's areas), whose precise role in language processing is still largely unknown. Another important finding was that RP amplitude in the left hemisphere differed as a function of the semantic category of the stimuli, providing evidence for the sensitivity of this component to semantic categorization. A tentative proposal is made with regard to the role of the basal extrastriate areas.

Adult↗
PubMed2000

Common basal extrastriate areas for the semantic processing of words and pictures.

OBJECTIVE: The recognition potential (RP) is an electrophysiological brain response which is sensitive to the semantic processing of meaningful stimuli. In this study we attempt to elucidate the topography and neural origin of the RP evoked by pictures and to compare it with the RP evoked by words. METHODS: Words, pictures, Chinese characters and control stimuli were presented to 20 subjects following the rapid stream stimulation procedure. The activity was recorded using 60 cephalic electrodes. RESULTS: We found a RP displaying its maximal amplitude at the left inferior parieto-occipital electrode (PO7) for words and at the right homologue electrode (PO8) for pictures and Chinese characters. Both the amplitude and the latency of the RP were larger in the case of words. A profile analysis indicated that the neural generators of the RP were common regardless of the type of stimulus, and a dipole analysis placed them about the lingual gyrus. CONCLUSIONS: Words and pictures share the same neural generators for the RP despite of subtle differences in lateralization. This is interpreted as an index of a multimodal semantic processing in basal extrastriate areas.

Adolescent↗
PubMed2000

Neurophysiological and neuropsychological differences related to performance and verbal abilities in subjects with mild intellectual disability.

The present study compared two group of subjects with intellectual disability. The 44 subjects in group 1 had equivalent verbal and performance IQs (67 and 64, respectively), while the 12 subjects in group 2 had an intellectual performance IQ which was > or = 10 points above their verbal performance IQ (80 and 65, respectively). The second group showed an alpha peak at a higher frequency and an evoked potential closer to normality. The decrease in the voltage of the P300 wave in group 1 was especially significant. The cognitive evoked potentials were also different between the two groups.

Child↗
PubMed1999

The recognition potential: An ERP index of lexical access.

Recognition potential (RP) is a brain electrical response that appears when a subject views recognizable images of words. However, it has yet to be determined whether the processes reflected by RP are related to orthographic or to semantic analysis. This study aimed to resolve this question by studying the RP evoked by orthographically correct stimuli that were devoid of meaning. Results showed RP not only to this type of stimuli, but also to others achieving lower levels in the reading process. Strikingly, however, the RP amplitude significantly differed in parallel with the levels of the reading processes attained by the stimuli, the amplitude of the RP progressively increasing as the level approached the semantic one, which showed the highest amplitude. These results not only confirm the replicability of RP, but also its promise of potential usefulness in the study and assessment of language perception.

Adult↗
PubMed1999

Insights from event-related potentials into the temporal and hierarchical organization of the ventral and dorsal streams of the visual system in selective attention.

The temporal and hierarchical relationships between the dorsal and the ventral streams in selective attention are known only in relation to the use of spatial location as the attentional cue mediated by the dorsal stream. To improve this state of affairs, event-related brain potentials were recorded while subjects attended simultaneously to motion direction (mediated by the dorsal stream) and to a property mediated by the ventral stream (color or shape). At about the same time, a selection positivity (SP) started for attention mediated by both streams. However, the SP for color and shape peaked about 60 ms later than motion SP. Subsequently, a selection negativity (SN) followed by a late positive component (LPC) were found simultaneously for attention mediated by both streams. A hierarchical relationship between the two streams was not observed, but neither SN nor LPC for one property was completely insensitive to the values of the other property.

Adolescent↗
PubMed1997

Event-related potentials during memorization of spatial locations in the auditory and visual modalities.

Event-related potential (ERP) studies of working memory have used delayed S1-S2 match-to-sample tasks in which S1 is held in memory for comparison with S2. ERP negativities in the S1-S2 interval have been interpreted either in terms of working memory operations, or in terms of general preparatory motor processing. Two experiments (N = 20 each) were carried out to explore the nature of ERP negativities in a visuospatial memory task and in an auditory spatial memory task, respectively. In the experimental condition, subjects had to memorize the location of S1 (S1-memorize) so as to respond whether S2 appeared in the same spatial location (S2-memorize). In the control condition, subjects were requested to ignore S1 (S1-passive), and to respond whether S2 matched or not a target location predetermined at the beginning of the trial block (S2-pressing). Results support the two main conclusions of Martin-Loeches et al. (Electroenceph. clin. Neurophysiol., 1994, 91: 363-373). Firstly, that the encoding into memory of spatial location is associated with an ERP negative wave over the brain areas putatively associated with the processing of sensory information (i.e. right parieto-occipital for the visual task; fronto-central and left temporal areas for the auditory task). Secondly, the P300 does not seem to be an important ERP feature related to spatial location encoding and retaining into memory. Despite the distinct scalp distribution of these memory-related, modality-specific ERP negativities, they also showed a considerable degree of temporal synchronicity across modalities.

Adolescent↗
PubMed1997

Encoding into working memory of spatial location, color, and shape: electrophysiological investigations.

Event-related potentials (ERP) were recorded while subjects memorized either the location, the color or the shape of stimuli which could be located in 1 of 4 positions relative to a central fixation point (top, bottom, left or right), be of 1 of 4 positions relative to a central fixation point (top, bottom, left or right), be of 1 of 4 colors (white, green, red or blue), and present 1 of 4 shapes (triangle, cross, circle or square). These ERP were compared to ERP recorded while subjects looked at the same stimuli but performed other control, nonmemory tasks. Only ERP corresponding to the memorization of spatial location showed a differential pattern which could be specifically attributed to memory encoding processes. This reveals an important difference in ERP modulation between a working memory subsystem for spatial location and other subsystem (or subsystems) for color or shape, which would provide evidence supporting the existence of different working memory subsystems for visual information in the brain.

Adolescent↗
PubMed1997

The phonological loop model of working memory: an ERP study of irrelevant speech and phonological similarity effects.

The phonological loop model for retention of auditory verbal material in working memory, developed by Baddeley, assumes that irrelevant speech and phonological similarity influence only one and the same element of the system--that is, the phonological short-term store. We tested this idea by recording event-related potentials (ERPs) to auditorily presented letters that were phonologically similar or dissimilar and were to be memorized in the presence of more or less disturbing irrelevant speech. Irrelevant speech and phonological similarity caused ERP effects with clearly different scalp topographies, indicating that these factors influence different brain systems and hence probably different cognitive elements. Moreover, ERPs indicated that the phonological similarity effect might involve processes at the level of phonological analysis. Our data also support recent suggestions that the irrelevant speech effect is not based on the phonological similarity between relevant and irrelevant material, but on the phonological variability within the irrelevant stream.

Adult↗
PubMed1995

Drug therapy and cerebral perfusion in obsessive-compulsive disorder.

Cerebral perfusion in a previously untreated patient with obsessive-compulsive disorder was studied qualitatively and semi-quantitatively with SPECT before, and during and 6 wk after treatment with clomipramine. The patient's symptoms disappeared while on medication and relapsed after drug withdrawal. At baseline, there was an increased perfusion ratio in the bilateral orbitofrontal, anterior cingular, frontotemporal and right caudate regions. These alterations disappeared during drug therapy. After treatment discontinuation and symptomatic relapse, the same pattern of hyperactivity was found. Semiquantitative measurements after treatment withdrawal showed a return to perfusion values similar to those observed before treatment in subcortical structures. In cortical areas, this level was not completely achieved. Subtraction SPECT images showed perfusion changes at the orbitofrontal, caudate and thalamic levels.

Adult↗
PubMedDate not supplied

[The P300 component of evoked potentials in the evaluation of schizophrenia: new evidence and future visions].

OBJECTIVE: To analyze the character as pathophysiological marker of the P300 component in the evaluation of schizophrenic illness. We therefore review clinical and neuropsychological evidence of studies in which this was used as a tool for evaluation to reach a diagnosis. DEVELOPMENT: The P300 component is useful for studying not only cognitive processes but also the physiopathology of complex disorders such as schizophrenia. This component reflects the state of functions of attention control and memory, both necessary for final evaluation of a stimulus. These cognitive functions become altered in schizophrenic illness, as is shown by abnormality in the generation of the P300 component. We review the most relevant results, which permit characterization of the many features of schizophrenia from genetic, symptom, morphology and neuropsychological studies in which the P300 component is particularly relevant. Similarly, we analyze current controversies due to the great heterogeneity of methodology and the nature of the illness itself. CONCLUSIONS: Current understanding allows us to establish that the P300 is a biological marker of relevant aspects of schizophrenia such as the genetic risk of suffering a psychotic episode, determine the type and gravity of the symptoms of the disease, as well as the degree of structural deterioration of the patient. The P300 component is sensitive to the effect of different neuroleptic drugs, on both the symptoms and neuropsychological functions of the patient. These findings let us suggest the P300 component as a valid marker for the evaluation of schizophrenia and the neuropsychological processes.

Adult↗