Biomedical subjects

David W Shucard

Publications and source records attributed to David W Shucard.

6 recordsLinked to original sources

PubMed2006

Working memory deficits in multiple sclerosis: comparison between the n-back task and the Paced Auditory Serial Addition Test.

Working memory (WM) deficits are common in multiple sclerosis (MS). The Paced Auditory Serial Addition Test (PASAT) is used frequently to measure WM in clinical settings. The n-back paradigm is used often in experimental studies of WM. One unique component of the n-back task is that it provides a measure of reaction time (RT), an additional behavioral index of processing speed and task difficulty. Despite the use of both tasks to measure WM, their common variance has not been documented. We tested 32 MS patients and 20 controls; performance measures were obtained for both tasks. Compared with controls, MS patients generally had poorer performance on both the PASAT and n-back task. MS patients also had slower RTs on the n-back than controls and showed more slowing than controls as a function of WM load. Correlational analyses showed a high correspondence between performance measures on the PASAT and n-back. Principal components analysis pointed to a common feature of the PASAT, n-back, and specific other neuropsychological measures, that is, processing speed. Although the PASAT and n-back were shown to have a significant amount of shared variance, each test has specific advantages and disadvantages for use in clinical populations.

Acoustic Stimulation↗

PubMed2004

The effects of covert attention and stimulus complexity on the P3 response during an auditory continuous performance task.

This study examined the effects of motor responding and stimulus complexity on the event-related potential (ERP) P3 amplitude and latency during an auditory continuous performance task (A-CPT). Subjects were presented with undegraded and degraded syllables during two experimental conditions. In the motor attention (MA) condition participants performed a button press to target syllables. In the covert attention (CA) condition, participants listened for target syllables without responding. The ERP P3 amplitude for targets during MA and CA showed the expected anterior-to-posterior scalp topography, with the greatest amplitude at Pz. Although amplitudes across all scalp sites were greater for MA than CA target P3 responses, both MA and CA targets had greater P3 amplitudes than the P3 for the nontarget syllables (NT). There was no effect of stimulus complexity (degraded vs. undegraded) on P3 amplitude. However, stimulus complexity did affect P3 latency. Degraded syllables elicited longer P3 latency than undegraded syllables for both the MA and CA conditions. The amplitude and topography findings show that when stimulus probability is controlled through the use of a CPT paradigm, a reliable P3 component is present even when the task does not require a motor response to target stimuli.

Acoustic Stimulation↗

PubMed2004

Tone probe event-related potential differences during a face recognition task in prepubertal children and Turner Syndrome girls.

Hormones have been shown to play a role in both cerebral development and neurocognitive function. Turner Syndrome (TS) provides the opportunity to study the effect of the lack of estrogen on neurocognitive development. In this study, event-related potential (ERP) differences were examined among 12 TS girls, 20 prepubertal control girls, and 20 prepubertal control boys during a face recognition memory task. Stage of puberty was determined by Tanner Scale rating and hormonal assay. ERPs to pairs of auditory probe stimuli were recorded from eight scalp sites while participants performed a faced recognition memory (FRM) task. For the N2 component of the ERP (which has previously been associated with evaluation of stimulus information, categorization difficulty, and attention), control boys displayed greater right versus left hemisphere amplitude, control girls displayed greater left versus right hemisphere amplitude, and there was no amplitude asymmetry for TS girls. Further, control girls had greater left hemisphere N2 amplitude than control boys and TS girls, and greater right hemisphere N2 amplitude than TS girls. The results suggest more right hemisphere activation during face recognition in boys, while the opposite pattern was present in control girls. In contrast, TS girls displayed no asymmetry, indicative of more uniform involvement of the left and right hemispheres during face recognition. These findings are consistent with differences in cortical organization related to face recognition memory processing among prepubertal control boys, girls, and TS girls. They also support the notion that sex differences in cognitive function are present prior to pubertal onset, and that lack of endogenous sex hormones (e.g., estrogen) during prenatal/perinatal development (i.e., for TS girls) may influence brain organization and, in turn, neurocognitive processes that relate to face recognition.

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PubMed2004

Working memory and processing speed deficits in systemic lupus erythematosus as measured by the paced auditory serial addition test.

As many as 66% of systemic lupus erythematosus (SLE) patients have been reported to have cognitive deficits. These deficits are often associated with information processing speed and working memory. Similarly, processing speed and working memory impairments are the hallmark of cognitive dysfunction in multiple sclerosis (MS). The Paced Auditory Serial Addition Test (PASAT) places high demands on processing speed and working memory. Fisk and Archibald, however, demonstrated that the total score of the PASAT does not accurately reflect impairments in these cognitive processes. They found that MS patients used a chunking strategy to obtain correct responses and reduce the cognitive demands of the task. In the present study, PASAT performance was examined for 45 SLE patients and 27 controls using alternative scoring procedures. Although the total number of correct responses did not differ between SLE and controls at the 2.4 or 2.0 s presentation rates, SLE patients had fewer dyads (correct consecutive responses) than controls at the faster rate, and more chunking responses than controls at both rates. Disease activity, disease duration, depression, fatigue, and corticosteroids could not account for these differences. The findings suggest that SLE patients, like MS patients, chunk responses more often than controls, and that this scoring procedure may better reflect the working memory and processing speed deficits present in SLE.

Acoustic Stimulation↗

PubMed2003

Single-trial latency variability of auditory evoked potentials may indicate immediate memory in the albino rat.

Fast habituation (FH) is defined as a decrease in auditory evoked potential (AEP) amplitude in response to the second of a pair of temporally juxtaposed (e.g. 1-s) tones. The degree of FH may depend, in part, on the subject's ability to anticipate the stimulus sequence. This paradigm has been used in our laboratory to study cognitive functioning in human subjects. We have also developed an animal model to investigate, more comprehensively, the anatomical and physiological basis of this phenomenon seen in human subjects. In the present investigation, we wished to determine the relationship between single-trial latency variability and AEP amplitude for two conditions: one for which FH is known to occur and one for which it is not present, due to the length of the interstimulus interval (ISI). Here AEPs were obtained to 40 pairs of 100-ms pure tone stimuli (70-dB SPL, 1- and 5-s ISI, 10-s interpair interval) from 19 chronically implanted, unanesthetized, restrained male Sprague-Dawley rats. The AEP latencies, amplitudes, and the single-trial latency variabilities were obtained for each component (P1, N1, P2 and N2). Findings indicated that FH was present for the 1-s ISI condition but not for the 5-s ISI condition. In addition, single-trial latency variability was negatively correlated with both Tones 1 and 2 AEP amplitudes in the 5-s ISI condition but only with Tone 1 amplitude in the 1-s ISI condition. Thus, single-trial latency variability predicted AEP amplitude only when FH did not occur. These results support earlier findings reported from our laboratory suggesting that the decrease in amplitude during FH is not related to increased variability in the time domain but rather to decreased neuronal output.

Acoustic Stimulation↗

PubMed2002

Covert auditory attention generates activation in the rostral/dorsal anterior cingulate cortex.

The anterior cingulate cortex (ACC) is believed to mediate conscious information processing or high-capacity attention. However, previous functional imaging studies have largely relied on tasks that involve motor function as well as attention. The work from our group utilizing an auditory continuous performance task demonstrated increased activity in a caudal division of the ACC that borders the supplementary motor area (SMA). Activity in this region was attributed to motor responding as well as attention. In the present study, we used (15)O H(2)O positron emission tomography (PET) to map brain activation during nonmotor, covert auditory attention. Our hypothesis was that a different region within the ACC, anterior to the SMA, would be active during covert attention (CA). Six men and six women were asked to monitor aurally presented syllables presented at a 1-sec interstimulus interval. During the CA condition, subjects were asked to continuously discriminate target (.19 probability) from nontarget stimuli. Simultaneous recording of event-related potentials (ERPs) confirmed the discrimination of target and nontarget stimuli and the allocation of attention capacity. Comparison of the monitored versus nonmonitored presentation of stimuli demonstrated significant activity in a rostral/dorsal division of the right ACC, anterior to SMA. Other regions of activation included the lateral prefrontal cortex and posterior superior temporal gyrus in the left hemisphere, consistent with neurocognitive models of language and vigilance. We conclude that a rostral/dorsal subdivision of the right ACC is specific for conscious attention during auditory processing, in contrast to premotor response formation.

Adult↗