Biomedical subjects

Juanita Todd

Publications and source records attributed to Juanita Todd.

8 recordsLinked to original sources

PubMed2006

Impaired detection of silent interval change in schizophrenia.

The reliably observed reduction in the mismatch negativity response to a change in sound duration in schizophrenia patients may be related to more widespread temporal processing impairments associated with the disorder. This study explored whether individuals with schizophrenia would show electrophysiological evidence of automatic deficits in the ability to detect changes in a regularly repeating interval between two tones. The established pattern was a repeating sequence of a pair of 50-ms tones with a 50-ms silent interval between them. In 8% of pairs, the silent interval between tones was increased to 125 ms. Significant differences in the response to the deviant tone pair in the patient group were consistent with impaired representation of the temporal relationship between sounds.

Acoustic Stimulation↗

PubMed2006

Preliminary investigation of gene expression profiles in peripheral blood lymphocytes in schizophrenia.

Schizophrenia is a heterogenous disorder that is phenomenologically characterised by a combination of negative, positive, and cognitive symptoms with variable expression in the course of illness. Here, we investigated differential gene expression in relation to age to address the heterogeneity of this disorder We used 6000 gene cDNA microarrays to generate gene expression profiles from peripheral blood lymphocytes from 14 individuals with schizophrenia and 14 non-psychiatric controls. Genes showing altered expression were identified and 18 genes with brain-related functions were altered, 4 of which, endothelial differentiation gene 2 (Edg-2), ezrin-radixin-moesin phosphoprotein 50 (EBP50), Myc-associated zinc finger protein (MAZ) and Tumor Necrosis Factor Receptor 2 (TNFR2), were confirmed by relative real-time PCR. Dendrograms were constructed using genes that showed significantly different expression (p<0.05) between groups based on median split of age dividing the matched pairs into distinct subclasses. Our findings suggest that distinct gene expression profiles in peripheral blood lymphocytes associated with schizophrenia phenotypes may provide a first step towards the biological classification of schizophrenia subtypes. The validity of this approach may lead to better methods of defining this enigmatic disease.

Adolescent↗

PubMed2006

Auditory sensory memory and the aging brain: A mismatch negativity study.

The mismatch negativity (MMN) component of the auditory event-related potential has been used in the past to study between group differences in the accuracy and retention of information in auditory sensory memory (ASM). The MMN is elicited by infrequent 'deviant' tones that differ from a repeating 'standard' tone. In the present study, the type of deviant and the time interval between tones (stimulus-onset asynchrony: SOA) were manipulated in a study of normal aging. MMN responses of an elderly (mean age = 69) and a young group (mean age = 21) to both a duration and a frequency deviant tone were measured at a short (450 ms) and long (3 s) SOA. A smaller and later MMN (recorded at Fz) was observed in the elderly relative to the young group across SOA and Deviant conditions. The results are consistent with an age-related deficit in the encoding of sound properties in ASM. However, analysis of the MMN reversal at the mastoids provides some support for the proposal that the elderly have an additional deficit related to the retention of information in ASM.

Acoustic Stimulation↗

PubMed2003

Impairment in activation of a frontal attention-switch mechanism in schizophrenic patients.

The present study addresses the difference in activities of frontal and temporal mismatch negativity (MMN) generators between healthy controls and schizophrenic patients. Auditory MMNs were measured from 13 medicated schizophrenic patients in a post-acute phase and 12 healthy controls. The probabilities of the standard stimuli were, in different experimental blocks, 95, 90, 80 or 70%. The mean amplitude of the MMN recorded at Fz was significantly smaller in schizophrenic patients than healthy controls only in the conditions with high probability of standard stimuli, while that recorded at mastoid sites was not different in any condition. The present study suggested that schizophrenic patients might fail to cause involuntary attention switch to stimulus change reflected in the lowered MMN amplitude recorded at Fz; whereas the patients might index an adequate detection of the deviant event reflected by the similar amplitude of MMN recorded at mastoid sites.

Adult↗

PubMed2003

Functional neuroanatomy of auditory mismatch processing: an event-related fMRI study of duration-deviant oddballs.

This study was designed to identify the neural networks underlying automatic auditory deviance detection in 10 healthy subjects using functional magnetic resonance imaging. We measured blood oxygenation level-dependent contrasts derived from the comparison of blocks of stimuli presented as a series of standard tones (50 ms duration) alone versus blocks that contained rare duration-deviant tones (100 ms) that were interspersed among a series of frequent standard tones while subjects were watching a silent movie. Possible effects of scanner noise were assessed by a "no tone" condition. In line with previous positron emission tomography and EEG source modeling studies, we found temporal lobe and prefrontal cortical activation that was associated with auditory duration mismatch processing. Data were also analyzed employing an event-related hemodynamic response model, which confirmed activation in response to duration-deviant tones bilaterally in the superior temporal gyrus and prefrontally in the right inferior and middle frontal gyri. In line with previous electrophysiological reports, mismatch activation of these brain regions was significantly correlated with age. These findings suggest a close relationship of the event-related hemodynamic response pattern with the corresponding electrophysiological activity underlying the event-related "mismatch negativity" potential, a putative measure of auditory sensory memory.

Adult↗

PubMed2003

Association between reduced duration mismatch negativity (MMN) and raised temporal discrimination thresholds in schizophrenia.

OBJECTIVE: The event-related potential known as mismatch negativity (MMN) is elicited whenever the auditory system detects a change against an invariant background of stimulation. A reduction in mismatch negativity is well established in schizophrenia. The present study explored the association between reduced duration mismatch negativity in schizophrenia and behavioural measures of temporal discrimination. METHOD: Mismatch negativity amplitude to duration increments (125 vs. 50 ms) was compared between individuals with schizophrenia and healthy controls. Mismatch negativity amplitude was also related to two behavioural measures of temporal discrimination (silent and filled intervals) for detecting changes in stimuli of similar duration. RESULTS: Patients produced higher discrimination threshold estimates and smaller amplitude mismatch negativity responses to temporally deviant stimuli. Temporal discrimination thresholds correlated with the amplitude of the phase reversal in mismatch negativity at the left mastoid such that patients who produced the highest thresholds produced the smallest mismatch response. CONCLUSIONS: Imprecise representations of the temporal properties of auditory stimuli can account for some of the reduction in mismatch negativity amplitude in some patients but additional factors clearly contribute. The results suggest that patients who do and do not exhibit temporal processing deficits on behavioural tasks produce different patterns of reduction in duration mismatch negativity.

Adult↗

PubMed2002

Duration mismatch negativity in biological relatives of patients with schizophrenia spectrum disorders.

BACKGROUND: One of the most consistent findings in schizophrenia research over the past decade is a reduction in the amplitude of an auditory event-related brain potential known as mismatch negativity (MMN), which is generated whenever a deviant sound occurs in a background of repetitive auditory stimulation. The reduced amplitude of MMN in schizophrenia was first observed for deviant sounds that differ in duration relative to background standard sounds, and similar findings have been observed for sounds that are deviant in frequency. The aim of this study was to determine whether first-degree relatives of schizophrenia patients show a similar reduction in MMN amplitude to duration deviants. METHODS: We measured MMN to duration increments (deviants 100 msec vs. standards 50 msec) in 22 medicated patients with a diagnosis in the schizophrenia spectrum, 17 individuals who were first-degree unaffected relatives of patients, and 21 healthy control subjects. RESULTS: Mismatch negativity amplitude was reduced in patients and relatives compared with control subjects. There were no significant differences between patients and relatives. In contrast, the subsequent positive component, P3a, was larger in relatives compared with patients. CONCLUSIONS: These findings suggest that a reduced MMN amplitude may be an endophenotype marker of the predisposition to schizophrenia.

Acoustic Stimulation↗

PubMedDate not supplied

Effects of noise and a stressor on head pain.

OBJECTIVE: Can causal relationships be established between negative affect (NA) and headaches, and noise (N) and headaches? Do NA and N interact to cause headaches? Do NA and N cause headaches by means of the same or different physiological mechanisms? Are the answers to these questions a function of diagnostic status? BACKGROUND: A functional model of chronic headaches has been proposed that seeks to understand the variance in headaches by focusing on the controlling variables, that is, the antecedents and consequences. This study is one in a series investigating the immediate antecedents of headaches, namely the trigger factors. DESIGN: Twenty-four subjects with migraine and 44 subjects with tension-type headache were randomly assigned to one of four experimental conditions defined by the presence or absence of two antecedent challenges, a stressor (S) designed to induce NA and N. METHODS: The S challenge consisted of difficult-to-solve anagrams accompanied by failure feedback. The N challenge consisted of 50 dB of white N. Laboratory sessions were divided into adaptation, baseline, challenge, and recovery phases. Responses were measured in terms of headache intensity ratings, forehead electromyographic activity, heart rate, blood pressure, and temporal pulse amplitude (TPA). RESULTS AND CONCLUSIONS: Both NA and N precipitated headaches. These two factors did not interact in triggering headaches. Headaches induced by N were associated with elevated TPA but headaches induced by NA were not associated with significant physiological changes. Diagnosis was not related to any of the outcomes.

Adolescent↗