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Biomedical subjects

M Kutas

Publications and source records attributed to M Kutas.

At least 37 records · Page 2Linked to original sources
PubMed1999

Limbic P300s in temporal lobe epilepsy with and without Ammon's horn sclerosis.

Limbic P300 potentials can be recorded within the mesial temporal lobes of patients with temporal lobe epilepsy (TLE). To delineate possible mechanisms of their generation and pathological alteration, we analysed limbic P300s in 55 TLE patients with and 29 without Ammon's horn sclerosis (AHS) and correlated their amplitudes with neuronal cell counts in 30 histopathological specimens. Limbic P300 amplitudes were reduced on the side of the epileptogenic focus only in patients with AHS. Moreover, in AHS patients, limbic P300 latencies were prolonged bilaterally; and in patients with left-sided AHS, amplitudes were reduced bilaterally. Both findings suggest bilateral functional deficits in TLE with unilateral AHS. Limbic P300 areas correlated significantly with neuronal densities of dentate gyrus granule cells but not hippocampal pyramidal cells in the CA1-4 (cornu ammonis) subfields. This finding points to a potential mechanism for the bilateral effects of unilateral AHS as both dentate gyri exhibit strong reciprocal contralateral connectivity.

Adolescent↗
PubMed1999

Semantic integration in reading: engagement of the right hemisphere during discourse processing.

We examined the brain areas involved in discourse processing by using functional MRI in 10 individuals as they read paragraphs, with or without a title, word by word for comprehension. Functional data were collected from 20 adjacent 5 mm axial slices. Discourse processing was associated with activation in inferior frontal and temporal regions of both cerebral hemispheres in the titled and untitled conditions. Moreover, there was substantially more right hemisphere activation for untitled than for the titled paragraphs. More specifically we found: (i) greater activation in the inferior temporal sulcus of both hemispheres for untitled than titled paragraphs; (ii) greater average volume of activation in response to untitled than titled paragraphs in the middle temporal sulcus of the right hemisphere and the reverse pattern in the left middle temporal sulcus. Consistent with previous studies of individuals with right hemisphere damage, we suggest that the right middle temporal regions may be especially important for integrative processes needed to achieve global coherence during discourse processing.

Adult↗
PubMed1999

An electrophysiological analysis of animacy effects in the processing of object relative sentences.

Event-related brain potentials (ERPs) were used to investigate how and when a semantic factor (animacy) affects the early analysis of a difficult syntactic structure, namely, object relative sentences. We contrasted electrophysiological and behavioral responses to two object relative types that were syntactically and lexically identical and varied only in the order of the component animate and inanimate nouns [Inanimate (Animate) vs. Animate (Inanimate)]. ERPs were recorded from 40 subjects to each word of 30 I(A) and 30 A(I) sentences that occurred randomly among a set of various other sentence types read for comprehension. ERP effects to the early noun animacy manipulation were observed beginning with the initial noun and extending past the main clause verbs. We interpret the timing and multitude of electrophysiological effects, including the N400, P600, and left-anterior negativity, as evidence that both semantic and syntactic, and perhaps other types of information, are used early during structural analysis and message-level computations as needed for comprehension.

Adult↗
PubMed1999

An electrophysiological analysis of modality-specific aspects of word repetition.

Priming effects to words are reduced when modality changes from study to test. This change was examined here using behavioral and electrophysiological measures of priming. During the study, half of the words were presented visually and half auditorally; during a subsequent lexical decision test, all words were presented visually. Lexical decisions were faster for within- than cross-modality repetitions. In contrast, modality influenced recognition only for low-frequency words. During lexical decision, event-related brain potentials were more positive to studied than unstudied words (200-500 ms). A larger and shorter duration effect was observed for within- than cross-modality repetitions (300-400 ms). This later effect is viewed as an electrophysiological index of modality-specific processing associated with priming. Results suggest that multiple events--both modality-specific and modality-nonspecific--underlie perceptual priming phenomena.

Adult↗
PubMed1998

Limbic ERPs predict verbal memory after left-sided hippocampectomy.

Surgical removal of the dominant medial temporal lobe regions runs a considerable risk of verbal memory deficits which may be compensated for postoperatively by corresponding regions in the non-dominant medial temporal lobe. We examined this possibility by recording event-related potentials (ERPs) to words from the medial temporal lobes of patients with left-sided temporal lobe epilepsy (TLE) undergoing presurgical evaluation. N400 amplitudes in the right anterior medial temporal lobe predicted the postoperative verbal recall performance of individual patients with surprising accuracy, indicating that intracranial recordings can be used to quantify the functional capacities of the right hemisphere that can compensate for the verbal memory deficits after loss of medial temporal lobe structures in the left hemisphere.

Adolescent↗
PubMed1998

When temporal terms belie conceptual order.

We conceive of time as a sequential order of real-world events, one event following another from past to present to future. This conception colours the way we speak of time ("we look forward to the time") and, as we show here, the way we process written statements referring to the temporal order of events, in real time. Terms such as 'before' and 'after' give us the linguistic freedom to express a series of events (real or imaginary) in any order. However, sentences that present events out of chronological order require additional discourse-level computation. Here we examine how and when these computations are carried out by contrasting brain potentials across two sentence types that differ only in their initial word ('After' X, Y versus 'Before' X, Y). At sites on the left frontal scalp, the responses to 'before' and 'after' sentences diverge within 300 ms; the size of this difference increases over the course of the sentences and is correlated with individual working-memory spans. Thus, we show that there are immediate and lasting consequences for neural processing of the discourse implications of a single word on sentence comprehension.

Brain Mapping↗
PubMed1998

Relationship between auditory P300 amplitude and age of onset of schizophrenia in older patients.

Auditory P300 amplitude reductions are well-established in young adults with schizophrenia. Little is known, however, regarding the P300 in older schizophrenia patients, especially those with late onset. We studied 28 middle-aged and elderly (mean age = 62.7 years) patients [14 with early onset schizophrenia (EOS) and 14 with late onset schizophrenia (LOS)] and 14 normal comparison (NC) participants using an auditory oddball paradigm. Event-related potentials were recorded from 15 scalp electrodes and six non-scalp sites. There were no significant differences between EOS and LOS groups in neuroleptic dosage, symptom severity, reaction times, target-detection accuracy, or N100 and N200 ERP measures. The EOS, but not the LOS, group had significantly smaller auditory oddball P300 amplitudes than the NC group. Twelve of the 14 LOS patients had P300 amplitudes in the normal range. Smaller P300 amplitudes were associated with earlier age of onset (r = 0.48), longer duration of illness (r = -0.49) and more severe alogia (r = -0.50). We conclude that P300 abnormalities in schizophrenia may be a marker for a disease subtype with early onset and more severe information-processing deficits.

Age of Onset↗
PubMed1998

Neural plasticity in the dynamics of human visual word recognition.

Repeated exposure to words leads to plastic changes in the nervous system throughout the lifespan, with the consequence that common words are processed more rapidly and accurately than rare words. Most behavior time measures correlate highly with the logarithm of a stimulus word's experiential frequency. Here, we demonstrate similar but earlier changes in the latency of a brain-generated evoked potential recorded over the left anterior scalp as individuals silently read sentences. We conclude that experience can speed the processing of some words by at least 50 ms within the first 335 ms of visual processing.

Brain↗
PubMed1998

An electrophysiological measure of priming of visual word-form.

Priming and recollection are expressions of human memory mediated by different brain events. These brain events were monitored while people discriminated words from nonwords. Mean response latencies were shorter for words that appeared in an earlier study phase than for new words. This priming effect was reduced when the letters of words in study-phase presentations were presented individually in succession as opposed to together as complete words. Based on this outcome, visual word-form priming was linked to a brain potential recorded from the scalp over the occipital lobe about 450 ms after word onset. This potential differed from another potential previously associated with recollection, suggesting that distinct operations associated with these two types of memory can be monitored at the precise time that they occur in the human brain.

Adult↗
PubMed1998

The covert interplay between perception and memory: event-related potential evidence.

Neurocognitive models of visual object identification have focussed on processes at the moment of identification, when perceivers can actually name what they see. Less well known is the timecourse of processes preceding and leading to actual identification. To track neuromental processes involved in visual identification, behavioral measures and event-related potentials (ERPs) were recorded in two experiments prior to, during and after the identification of fragmented objects, half of which had been shown in their complete versions in a previous study phase. Each object was revealed in a sequence of frames wherein the object was represented by an increasingly less and less fragmented image up to the complete version. A shift in ERPs, around 300 ms and beyond, from negativity to positivity, marked the transition from non-identification to identification. However, while for new stimuli such a shift appeared abruptly from non-identification to identification, for recently-studied objects a late positive wave emerged in response to unidentified fragments at a level just prior to overt identification. Thus, ERPs reflected covert processes associated with a successful match between the current visual information and episodic recently-stored memory traces, which predicted overt identification.

Adult↗
PubMed1998

The N400 in a semantic categorization task across 6 decades.

OBJECTIVES: To characterize the effects of normal aging on the amplitude, latency and scalp distribution of the N400 congruity effect. METHODS: Event-related brain potentials (ERPs) were recorded from 72 adults (half of them men) between the ages of 20 and 80 years (12/decade) as they performed a semantic categorization task. Participants listened to spoken phrases (e.g. 'a type of fruit' or 'the opposite of black') followed about 1 s later by a visually-presented word that either did or did not fit with the sense of the preceding phrase; they reported the word read and whether or not it was appropriate. ERP measurements (mean amplitudes, peak amplitudes, peak latencies) were subjected to analysis of variance and linear regression analyses. RESULTS: All participants, regardless of age, produced larger N400s to words that did not fit than to those that did. The N400 congruity effect (no-fit ERPs - fit ERPs) showed a reliable linear decrease in the amplitude (0.05-0.09 microV per year, r = 0.40) and a reliable linear increase peak latency (1.5-2.1 ms/year, r = 0.60) with age. CONCLUSIONS: In sum, the N400 semantic congruity effect at the scalp gets smaller, slower and more variable with age, consistent with a quantitative rather than qualitative change in semantic processing (integration) with normal aging.

Acoustic Stimulation↗
PubMed1998

Context effects in a category verification task as assessed by event-related brain potential (ERP) measures.

This study examined the extent to which decisions about category membership (between category structure) are dependent on or dissociable from the typically structure (within category structure) of categories. To this end, behavioral and event-related brain potential (ERP) measurements were obtained in a category verification task that incorporated a context manipulation (list composition effect) that was previously shown to affect membership verification. In a German and an American English version of the experiment, pairs of words were presented and subjects were asked to decide whether or not the second word was an exemplar of the superordinate indicated by the first word. Both versions yielded similar results. The behavioral data showed that both typicality and context manipulation affected the verification times for the true exemplars. Furthermore, atypical true exemplars were affected more by context manipulation than mere typical ones. By contrast, the N400 component of the ERPs elicited by the true exemplars was influenced by typicality, but invariant in the face of the context manipulation. These results underscore the previously shown dissociation between reaction times and N400 changes and suggest that category membership decision (as reflected in verification times) and semantic relatedness or typicality of an exemplar (as reflected in N400 modulation) can vary independently from each other and, therefore, likely index the activity of different brain systems.

Adult↗
PubMed1998

Minding the body.

As we continue to elucidate relationships between neural structures and cognitive functioning in this Decade of the Brain, it is important not to lose sight of the larger context. The brain is but one component of the complex system that is the body. We take in information and interact with the world through our bodies, and our bodies change with--and in some cases change--cognitive and emotional processing. In this introductory paper, we present an overview of a broad range of psychophysiological techniques: electroencephalography, event-related potentials, magnetoencephalography, positron emission tomography, optical imaging, functional magnetic resonance imaging, electromyograms, eye tracking, pupillometry, cardiovascular measures, and electrodermal activity. These techniques not only differ in their temporal and spatial resolutions but also in the physiological and psychological processes to which they are sensitive. With respect to the system as a whole, these techniques are thus complementary. Combining measures--old and new, central and peripheral--ultimately provides the most inferential power for attacking the questions we hope to answer with all psychophysiological measures in our quest to understand the nature of the relationship between the mind and the body.

Animals↗
PubMed1998

Neurophysiological evidence for visual perceptual categorization of words and faces within 150 ms.

The nature and early time course of the initial processing differences between visually matched linguistic and nonlinguistic images were studied with event-related potentials (ERPs). The first effect began at 90 ms when ERPs to written words diverged from other objects, including faces. By 125 ms, ERPs to words and faces were more positive than those to other objects, effects identified with the P150. The amplitude and scalp distribution of P150s to words and faces were similar. The P150 seemed to be elicited selectively by images resembling any well-learned category of visual patterns. We propose that (a) visual perceptual categorization based on long-term experience begins by 125 ms, (b) P150 amplitude varies with the cumulative experience people have discriminating among instances of specific categories of visual objects (e.g., words, faces), and (c) the P150 is a scalp reflection of letterstring and face intracranial ERPs in posterior fusiform gyrus.

Adolescent↗
PubMed1998

Memory changes with normal aging: behavioral and electrophysiological measures.

We examined performance in young and elderly on an implicit (lexical decision) and an explicit (recognition) memory test. The difference in lexical decision times between old and new words was equivalent in the two groups, although the elderly were slower. In both groups, recognition accuracy (lower in the elderly) was higher following semantic than nonsemantic encoding, whereas lexical decision times were unaffected. Divergent brain potentials for old and new words during lexical decisions constituted a repetition effect, which reflected greater positivity (200-800 ms) for old words, particularly over the left hemisphere; this effect was smaller and later in the elderly. An electrophysiological marker of enhanced recollection for words from the semantic encoding task took the form of a left-sided positivity (500-800 ms). The effect was smaller in the elderly than the young, providing an additional index of their impaired recognition processes.

Adolescent↗
PubMed1997

N400 abnormalities in late life schizophrenia and related psychoses.

The N400, an event-related brain potential (ERP) sensitive to semantic congruity, has been reported to have increased latency and/or reduced amplitude in young adults with schizophrenia. Little is known, however, regarding the N400 in older schizophrenia patients, especially those with late onset. We studied 18 middle-aged and elderly patients with schizophrenia and related psychoses (nine with early-onset psychosis (EOP) and nine with late-onset psychosis (LOP)), and nine normal comparison (NC) subjects. Subjects read words which were semantically incongruent (50%) or congruent (50%) with a preceding spoken phrase which defined either an antonymic or categorical relationship. The LOP group had a significantly later peak latency of the N400 congruity effect compared to the NC group. Seven of 18 psychosis patients, but none (0/9) of the normal subjects, had an abnormal latency or amplitude (p = 0.04), measured at T6 (right temporal). Smaller amplitudes were associated with more severe negative symptoms (rp = 0.58; p = 0.01). N400 abnormalities in older schizophrenia patients likely reflect abnormal processing of semantic information.

Adult↗
PubMed1997

What's in a pause: event-related potential analysis of temporal disruptions in written and spoken sentences.

Two experiments examined the effects of disrupting the temporal patterns that develop during sentence reading and listening. Sentences were presented either visually, one word at a time (Experiment 1) or as natural speech (Experiment 2). Half of the sentences were familiar (proverbs or idioms) while the other half were constructed anew for these experiments. Within half the sentences, there was an unexpected 600-ms delay between the final two words. In both modalities, the amplitude of the N400 component of the event-related brain potential (ERP) to sentence final words was larger for unfamiliar than familiar sentences. The results in the two modalities differed, however, in that a Contingent Negative Variation (CNV) developed during the delay interval in the visual modality, whereas in the auditory modality the delay was marked by an emitted potential. The present results show that temporal patterns are processed differently in natural speech and in reading words presented one at a time in the center of a computer screen.

Acoustic Stimulation↗