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Biomedical subjects

W Ritter

Publications and source records attributed to W Ritter.

At least 73 records · Page 4Linked to original sources
PubMed1995

Event-related potential and behavioral correlates of semantic processing in Alzheimer's patients and normal controls.

In normal young adults, N400 amplitude varies inversely with the extent to which a word has been primed by its preceding semantic context. Based on a series of behavioral studies, it appears that in Probable Alzheimer's patients (PAD) the organization of semantic memory is disrupted such that specific items within a category lose their distinction, although superordinate information remains relatively intact. The present study examined whether the N400 gradient which has been found with normal young adults would also reflect this loss of discriminability among semantically related items in PAD patients. Ten normal young adults, 10 normal elderly, and 6 "mild" PAD patients made speeded (but accurate) sense/nonsense decisions to the terminal words of a series of highly constrained sentence contexts. The terminal words belonged to one of four stimulus types which varied as a function of relatedness to a highly expected word. Counter to our predictions, N400 amplitude was identically responsive to semantic relatedness in the young normal and PAD groups, but was characterized differently in the normal elderly. Given the significantly greater number of errors committed by PAD patients, we concluded that their disruption in semantic processing occurs at some point between the elicitation of N400 and the generation of the reaction time response. The anomalous N400 pattern in the normal elderly appeared to be strategy related and superimposed upon an otherwise normal semantic network.

Adult↗
PubMed1995

The mismatch negativity of event-related potentials as a probe of transient auditory memory: a review.

The use of the mismatch negativity as a probe to study the memory upon which it depends is reviewed. Topics about the memory include its duration, its capacity, the kind of information that can be stored in the memory, how the information is stored, whether the memory is accessed in parallel or in series, whether it is hard-wired or can be modified by experience, and its relationship to sensory memory.

Evoked Potentials, Auditory↗
PubMed1995

Working memory and preparation elicit different patterns of slow wave event-related brain potentials.

Some event-related brain potential (ERP) studies of working memory have used delayed match-to-sample designs in which a stimulus (S1) is held in memory for comparison with a subsequent stimulus (S2). During the S1-S2 interval, ERP slow negatives varied with both the type and amount of material held in working memory. One interpretation is that these slow waves index working memory operations. An alternative explanation is that they only reflect general preparatory processing for the response to S2. To decide between these explanations, we used two visual processing tasks that required similar preparation for S2. In one task, visual memory rehearsal operations were required. During the S1-S2 interval, there were clear differences between the amplitudes, topographies, and the effect of information load on the slow waves in two tasks, thus ruling out preparation only as an explanation.

Adult↗
PubMed1995

Auditory sensory ("echoic") memory dysfunction in schizophrenia.

OBJECTIVE: Studies of working memory dysfunction in schizophrenia have focused largely on prefrontal components. This study investigated the integrity of auditory sensory ("echoic") memory, a component that shows little dependence on prefrontal functioning. METHOD: Echoic memory was investigated in 20 schizophrenic subjects and 20 age- and IQ-matched normal comparison subjects with the use of nondelayed and delayed tone matching. RESULTS: Schizophrenic subjects were markedly impaired in their ability to match two tones after an extremely brief delay between them (300 msec) but were unimpaired when there was no delay between tones. CONCLUSIONS: Working memory dysfunction in schizophrenia affects brain regions outside the prefrontal cortex as well as within.

Acoustic Stimulation↗
PubMed1995

Prostaglandin D2-induced bronchoconstriction is mediated only in part by the thromboxane prostanoid receptor.

Prostaglandin D2 (PGD2) is a potent bronchoconstrictor, and is thought to have a role in the pathogenesis of asthma. PGD2 causes vasodilation acting via the prostaglandin (DP) receptor on vascular smooth muscle, and myocontraction acting via the thromboxane (TP) receptor on bronchial smooth muscle. To determine the relative contribution of these mechanisms we have studied the degree to which a potent TP receptor antagonist inhibits PGD2-induced bronchoconstriction. Twelve atopic asthmatic subjects underwent baseline PGD2 bronchial challenges to determine the cumulative concentration of PGD2 required to reduce forced expiratory volume in one second (FEV1) by 20%. At four subsequent randomized visits, subjects received this concentration of PGD2 90 min after dosing with placebo or 20, 50 or 100 mg of BAY u 3405, a potent competitive TP receptor antagonist. Serum was taken for drug assay at 90 min. After each dose of PGD2, FEV1 was measured for 30 min, and the area under the percentage fall in the FEV1/time curve (AUC) was calculated. The mean +/- SEM AUC for placebo was 414 +/- 68, and for the 20, 50 and 100 mg doses of BAY u 3405 was 169 +/- 33, 173 +/- 59 and 135 +/- 63, respectively. There were no significant differences between the AUCs for any of the drug doses, whilst all three doses were significantly different from placebo. The plateau response achieved with increasing doses of the antagonist suggests complete blockade of the TP receptor. These data demonstrate that thromboxane receptor blockade only partially inhibits the airway narrowing response to PGD2, and support the existence of a vascular component to PGD2-induced acute airway narrowing in asthma.

Adult↗
PubMed1995

Event-related potential correlates of early processing in normal aging.

Auditory event-related potentials were recorded from normal elderly and young adult subjects during simple reaction time and discrimination conditions. In both response conditions, the stimuli were randomly presented, as in an auditory "oddball" paradigm. It was found that NA, an index of early information processing, was significantly delayed in the elderly. Although the latency of N1 was not significantly different between the groups, the latencies of N2 and P3 were significantly longer for the aged subjects. The amplitudes of N1, NA1, NA2 and N2 showed no group differences. The raw amplitude of P3 showed a group difference in topography: Pz was greater than Fz for the young group, but not for the aged. When the amplitudes of NA1, NA2, and P3 were scaled, however, the topography of these components showed no significant group differences. These findings suggest that the age-related slowing of later ERP components and behavior may be partially accounted for by delays in early attention dependent perceptual processes, as indexed by NA.

Adult↗
PubMed1994

Early and late cognitive event-related potentials mark stages of HIV-1 infection in the drug-user risk group.

HIV-1 (Human immunodeficiency virus) infection of the brain causes delays in auditory event-related potential (ERP) components. We recorded auditory ERPs from 38 former parenteral drug users (PDUs) at three stages of HIV-1 infection: seronegative; seropositive; stage II; and seropositive, stage IV. There were five response conditions: Go Nogo, Count, Simple Response, Simple Count, and Ignore. P3 peak latencies were significantly delayed and P3 amplitudes were significantly reduced for all seropositives, including asymptomatics, when compared to PDU seronegative controls. In contrast, the P1 and N1 peak latency measures were delayed only for seropositives with acquired immunodeficiency syndrome (AIDS) qualifying illnesses. There was a significant negative correlation between the CD4 count and the latency of P1, N1, and the MMN. Also, increased P1 and N1 amplitudes correlated with indices of disease progression (Choice RT and CD4 counts, respectively). The results extend previous findings by clarifying the pattern of auditory ERP markers of disease progression. Early, as well as late, brain involvement caused by HIV-1 is marked by delays and decreased amplitudes in cognitive components. In addition, late brain involvement is marked by delays and increased amplitudes in specific, automatic, and/or obligatory components.

AIDS Dementia Complex↗
PubMed1994

Implicit retrieval processes in cued recall: implications for aging effects in memory.

Aging produces deficits in what has come to be called explicit or direct memory, in which subjects must consciously retrieve information from long-term memory. In contrast, many studies have shown that when implicit or indirect memory is tested, old and young subjects perform equivalently. The present study manipulated orienting instructions (structural vs. semantic) for indirect (stem completion) and direct (cued recall) memory tasks for both young and old subjects. Contrary to previous research, older subjects produced equivalent performance to young subjects on the direct test as well as on the indirect test, and performance of both groups was worse in the direct than indirect test. In addition, semantic orienting activity at study led to greater learning on the indirect test than structural orienting for both groups, although the levels of processing effect was greater for the direct test. We attribute the unexpected lack of age difference on the direct test to its difficulty, which led subjects to adopt an implicit (generate + recognize) rather than an explicit retrieval strategy during the cued recall task. Because the elderly are not impaired with regard to either implicit retrieval or recognition, this strategy produced equivalent performance in the two groups.

Adult↗
PubMed1994

Event-related brain potential evidence for a verbal working memory deficit in multiple sclerosis.

Memory deficits are frequently identified in patients with multiple sclerosis. Both working (short-term) and long-term memory appear affected, particularly on free-recall tasks. The focus of our study was to examine neurophysiological correlates of working memory processes and to identify the specific components responsible for the working memory deficits reported in multiple sclerosis. Event-related brain potentials (ERPs) were recorded from the scalp of mildly afflicted multiple sclerosis patients and their matched normal controls during the performance of phonological and visuo-spatial working memory tasks. Neuropsychological test, behavioural performance and ERP data all indicated that verbal working memory is especially susceptible to impairment by multiple sclerosis, while visuospatial working memory is less susceptible. The pattern of results further indicated that the verbal working memory dysfunction in multiple sclerosis is at least partially due to impairment in the phonological loop, a rehearsal mechanism for retaining verbal information in working memory.

Adult↗
PubMed1993

Impairment of early cortical processing in schizophrenia: an event-related potential confirmation study.

Abnormalities of auditory information processing represent a core feature of schizophrenic psychopathology. Event-related potentials (ERP) provide an objective index of the information processing deficits associated with schizophrenia and a tool for investigation of the underlying pathophysiology. The best established abnormality is a decrease in the amplitude of auditory P300. In an "oddball" paradigm, P300 is preceded by a series of earlier, negative-polarity ERP components that index discrete, prior information-processing events. The earliest such component, mismatch negativity (MMN), is elicited whenever a deviant, "oddball" stimulus interrupts a sequence of repetitive standard stimuli. MMN is generated principally within primary auditory cortex or adjacent structures on the superior temporal plane, suggesting that it indexes the earliest cortical event in the cognitive processing of auditory information. In the present study, MMN was studied in a group of 14 chronic schizophrenic subjects relative to 12 age- and IQ-matched normal controls in a passive auditory oddball paradigm in order to test the hypothesis that auditory information processing is impaired in schizophrenia, even at the level of primary sensory cortex. Schizophrenic subjects showed a significant reduction in MMN amplitude relative to controls, with a trend toward a greater deficit on the left than the right side. The finding of impaired MMN generation in schizophrenia suggests that information processing is impaired even at the level of auditory cortex and that the pathophysiological processes underlying information processing dysfunction in schizophrenia are widespread throughout the cortex, rather than limited to high-order association cortex such as prefrontal or mesial temporal cortex.

Adult↗
PubMed1993

The effect of BAY u 3405, a thromboxane receptor antagonist, on prostaglandin D2-induced nasal blockage.

BACKGROUND: Nasal lavage and challenge studies in allergic rhinitis implicate prostaglandin (PG) D2 in the genesis of nasal blockage. PG D2 is known to act via at least two receptors, the thromboxane prostanoid receptor and the PG D2 prostanoid (DP) receptor; the lower airway effects are mediated chiefly by the TP receptor. The receptor involved in the genesis of PG D2-induced nasal blockage is unknown. BAY u 3405 is a potent selective competitive TP receptor antagonist, which inhibits the lower airway response to PG D2, and shifts the dose-response curve to the right by up to 16-fold. METHODS: The efficacy of a single oral dose of 20 mg of BAY u 3405 was examined in comparison with PG D2 nasal insufflation in a randomized, double-blind, placebo-controlled crossover study, with objective measurement of nasal resistance by active posterior rhinomanometry. RESULTS: BAY u 3405 afforded no protection against PG D2-induced nasal blockage. CONCLUSIONS: This suggests that PG D2-induced nasal blockage may be mediated by the DP receptor rather than the TP receptor and that TP receptor antagonists are unlikely to be of benefit in the treatment of allergic rhinitis. In vivo investigation with specific potent DP receptor antagonists is awaited.

Adult↗
PubMed1993

Event-related potentials as indicators of repetition priming in young and older adults: amplitude, duration, and scalp distribution.

Event-related brain potentials (ERPs) were recorded in young and older adults in an indirect repetition priming paradigm. Compared with the young adults, the older adults' ERP repetition effect was larger and of longer duration, due entirely to greater amplitude elicited by the repeated item. These data suggest that, although indirect memory (as indexed by a robust ERP repetition effect) appeared to be intact in the older adult, the possibility exists for qualitative age-related differences consistent with inefficient and/or additional processing of the repeated item.

Adult↗
PubMed1992

Endogenous event-related potentials as indices of dementia in multiple sclerosis patients.

Auditory event-related potentials (ERPs) were recorded in a "double oddball" paradigm requiring an easy and a hard pitch discrimination from multiple sclerosis (MS) patients with and without dementia, and a group of age and sex matched normal subjects. Cognitive function was assessed by a short battery of neuropsychologic (NP) tests, and the two groups of MS patients were selected on the basis of substantial non-overlapping degrees of cognitive deficit in the demented as compared to the non-demented group. The N100, P200 and P300 ERP components were longer in latency in the demented patients, and the N100-P300 interval was prolonged as well, compared to the non-demented patients, whose ERP latencies did not differ from those of the normal subjects. Increased P300 latency was associated with poorer performance on the NP tests, especially those sensitive to impairment of learning and retrieval from memory. The reaction times of both patient groups were prolonged as compared to the controls, whereas the accuracy of the demented patients was significantly poorer than that of the non-demented patients.

Adult↗
PubMed1992

Event-related potentials to repetition and change of auditory stimuli.

The major intent of this study was to compare the role of stimulus repetition and change in the elicitation of the MMN, an ERP component specific to stimulus change, and N2b, usually partially overlapping the MMN when stimuli are attended. Event-related potentials were recorded in one set of conditions where subjects ignored the stimuli and read a book, and in another set of conditions where subjects counted stimuli designated as targets. Stimuli were delivered in 4 ways, the common feature between all these conditions being the occurrence of infrequent events at a probability of 0.20: (1) an oddball paradigm with 1 deviant, (2) an oddball paradigm with 2 deviants, each with a probability of 0.10, (3) a regular alternation of tones of 2 pitches where either of the 2 tones infrequently repeated (P = 0.20), and (4) a random presentation of tones of 5 different pitches, where any of the 5 tones infrequently repeated (P = 0.20). In the count conditions, the infrequent events were designated as targets. It was found that the MMN was elicited by stimulus change and not stimulus repetition in the ignore and count conditions, whereas the N2b was elicited by both stimulus changes and repetitions in the count conditions. It was also possible, in the count conditions, to disentangle the part of the late positive complex which is related to stimulus deviation and the part which is related to stimulus significance (target).

Acoustic Stimulation↗
PubMed1992

Distinctions and similarities among working memory processes: an event-related potential study.

Working memory has been conceptualized as consisting of a number of components, such as an articulatory loop for rehearsing verbal material, a visuo-spatial sketch pad for maintaining visual images and a central executive that controls which information is made available for conscious processing. We recorded event-related brain potentials (ERPs) from normal human subjects while they maintained either visuo-spatial or phonological material in short-term memory for a 5-s interval. The results indicated that specialized brain systems for short-term storage of phonological and visuo-spatial information could be identified on the basis of marked differences between the topographies and morphologies of the ERP components elicited during these two types of short-term memory. The differences emerged during early encoding stages and continued through later retention stages.

Adult↗