PubMed Health⌕ Search

Biomedical subjects

L Sprague

Publications and source records attributed to L Sprague.

14 recordsLinked to original sources
PubMed2002

Mismatch negativity to single and multiple pitch-deviant tones in regular and pseudo-random complex tone sequences.

OBJECTIVES: To determine whether the process responsible for the mismatch negativity (MMN) might be involved in the analysis of temporal sound patterns for information. METHODS: Synthesized musical instrument tones of 'clarinet' timbre were delivered in a continuous sequence at 16 tones/s, such that there was virtually no N1 potential to each individual tone. The standard sequence comprised 4 or 5 adjacent notes of the diatonic scale, presented either as a regularly repeated, rising pattern or pseudo-randomly. The deviant stimuli were 1-5 consecutive tones of higher pitch than the standards. RESULTS: A MMN was evoked by a single deviant tone, 1 or 5 semitones above the pitch range of the standards. The response to the 5-semitone deviant was significantly larger (mean of 7.3 microV) when the standard pattern was regular as compared with pseudo-random. The MMN latency, on the other hand, was only influenced by the magnitude of pitch deviation. A second MMN was evoked by a second deviant tone, immediately (SOA 62.5 ms) following the first. Further consecutive MMNs were not consistently evoked. CONCLUSIONS: The large amplitude of these MMNs can be attributed to the use of complex tones, continuous presentation and a rapid rate of pitch changes, such that no waveform subtraction was required. Over and above the probability with which each individual tone occurs in the standard sequence, the mismatch process is influenced by its temporal structure, i.e. can be regarded as a temporal pattern analyzer. Contrary to the findings of some other groups, we found that two consecutive deviants can evoke an MMN, even at high rates of presentation such that both occur within the postulated 'temporal window of integration' of ca. 170 ms. These findings suggest that the mismatch process might be involved in the extraction of sequential information from repetitive and non-repetitive sound patterns.

Acoustic Stimulation↗
PubMed2002

Electrophysiological evidence for a defect in the processing of temporal sound patterns in multiple sclerosis.

OBJECTIVES: To assess the processing of spectrotemporal sound patterns in multiple sclerosis by using auditory evoked potentials (AEPs) to complex harmonic tones. METHODS: 22 patients with definite multiple sclerosis but mild disability and no auditory complaints were compared with 15 normal controls. Short latency AEPs were recorded using standard methods. Long latency AEPs were recorded to synthesised musical instrument tones, at onset every two seconds, at abrupt frequency changes every two seconds, and at the end of a two second period of 16/s frequency changes. The subjects were inattentive but awake, reading irrelevant material. RESULTS: Short latency AEPs were abnormal in only 4 of 22 patients, whereas long latency AEPs were abnormal to one or more stimuli in 17 of 22. No significant latency prolongation was seen in response to onset and infrequent frequency changes (P1, N1, P2) but the potentials at the end of 16/s frequency modulations, particularly the P2 peaking approximately 200 ms after the next expected change, were significantly delayed. CONCLUSION: The delayed responses appear to be a mild disorder in the processing of change in temporal sound patterns. The delay may be conceived of as extra time taken to compare the incoming sound with the contents of a temporally ordered sensory memory store (the long auditory store or echoic memory), which generates a response when the next expected frequency change fails to occur. The defect cannot be ascribed to lesions of the afferent pathways and so may be due to disseminated brain lesions visible or invisible on magnetic resonance imaging.

Adult↗
PubMed2001

Primary care case management: lessons for Medicare?

This paper looks at primary care case management (PCCM) as a tool that states have used to manage the delivery of care to their Medicaid populations, an alternative to contracting with commercial managed care plans. PCCM has proved a flexible means of advancing state policy goals, including quality improvement, disease management, and coverage of special-needs populations. The paper considers provider and beneficiary perspectives on PCCM as well as state agency objectives and accomplishments. Finally, it raises the question of adapting the PCCM model for Medicare. Speakers at the accompanying Forum session will expand on these topics.

Budgets↗
PubMed2000

Spectro-temporal analysis of complex tones: two cortical processes dependent on retention of sounds in the long auditory store.

OBJECTIVES: To examine whether two cortical processes concerned with spectro-temporal analysis of complex tones, a 'C-process' generating CN1 and CP2 potentials at cf. 100 and 180 ms after sudden change of pitch or timbre, and an 'M-process' generating MN1 and MP2 potentials of similar latency at the sudden cessation of repeated changes, are dependent on accumulation of a sound image in the long auditory store. METHODS: The durations of steady (440 Hz) and rapidly oscillating (440-494 Hz, 16 changes/s) pitch of a synthesized 'clarinet' tone were reciprocally varied between 0.5 and 4.5 s within a duty cycle of 5 s. Potentials were recorded at the beginning and end of the period of oscillation in 10 non-attending normal subjects. RESULTS: The CN1 at the beginning of pitch oscillation and the MN1 at the end were both strongly influenced by the duration of the immediately preceding stimulus pattern, mean amplitudes being 3-4 times larger after 4.5 s as compared with 0.5 s. CONCLUSIONS: The processes responsible for both CN1 and MN1 are influenced by the duration of the preceding sound pattern over a period comparable to that of the 'echoic memory' or long auditory store. The store therefore appears to occupy a key position in spectro-temporal sound analysis. The C-process is concerned with the spectral structure of complex sounds, and may therefore reflect the 'grouping' of frequency components underlying auditory stream segregation. The M-process (mismatch negativity) is concerned with the temporal sound structure, and may play an important role in the extraction of information from sequential sounds.

Acoustic Stimulation↗
PubMed2000

Auditory evoked potentials to spectro-temporal modulation of complex tones in normal subjects and patients with severe brain injury.

In order to assess higher auditory processing capabilities, long-latency auditory evoked potentials (AEPs) were recorded to synthesized musical instrument tones in 22 post-comatose patients with severe brain injury causing variably attenuated behavioural responsiveness. On the basis of normative studies, three different types of spectro-temporal modulation were employed. When a continuous 'clarinet' tone changes pitch once every few seconds, N1/P2 potentials are evoked at latencies of approximately 90 and 180 ms, respectively. Their distribution in the fronto-central region is consistent with generators in the supratemporal cortex of both hemispheres. When the pitch is modulated at a much faster rate ( approximately 16 changes/s), responses to each change are virtually abolished but potentials with similar distribution are still elicited by changing the timbre (e.g. 'clarinet' to 'oboe') every few seconds. These responses appear to represent the cortical processes concerned with spectral pattern analysis and the grouping of frequency components to form sound 'objects'. Following a period of 16/s oscillation between two pitches, a more anteriorly distributed negativity is evoked on resumption of a steady pitch. Various lines of evidence suggest that this is probably equivalent to the 'mismatch negativity' (MMN), reflecting a pre-perceptual, memory-based process for detection of change in spectro-temporal sound patterns. This method requires no off-line subtraction of AEPs evoked by the onset of a tone, and the MMN is produced rapidly and robustly with considerably larger amplitude (usually >5 microV) than that to discontinuous pure tones. In the brain-injured patients, the presence of AEPs to two or more complex tone stimuli (in the combined assessment of two authors who were 'blind' to the clinical and behavioural data) was significantly associated with the demonstrable possession of discriminative hearing (the ability to respond differentially to verbal commands, in the assessment of a further author who was blind to the AEP findings). Behavioural and electrophysiological findings were in accordance in 18/22 patients, but no AEPs could be recorded in two patients who had clear behavioural evidence of discriminative hearing. The absence of long-latency AEPs should not, therefore, be considered indicative of complete functional deafness. Conversely, AEPs were substantially preserved in two patients without behavioural evidence of discriminative hearing. Although not necessarily indicative of conscious 'awareness', such AEP preservation might help to identify sentient patients who are prevented by severe motor disability from communicating their perception.

Acoustic Stimulation↗
PubMed1992

Duration of fever during treatment of infective endocarditis.

We reviewed the duration of fever among 123 patients treated for infective endocarditis at University Hospitals of Cleveland between 1972 and 1984. One half of these patients became afebrile within 3 days after initiation of antibiotic therapy and nearly three quarters were afebrile after 1 week of therapy. After 2 weeks of therapy, nearly 90% had defervesced. Endocarditis due to Staphylococcus aureus or gram-negative bacilli, and culture-negative endocarditis, were associated with prolonged fever. Microvascular phenomena, major vessel embolization, or vegetations seen on 2-D echocardiogram also were associated with prolonged fever. Multivariate analysis revealed that only microvascular phenomena or major vessel embolization were independently associated with longer duration of fever. Endocarditis-associated mortality among patients who remained febrile after 1 week of therapy was 18%, and this was greater than the 2% mortality among patients who defervesced (p less than 0.002). These data suggest that prolonged fever during treatment of infective endocarditis is often due to tissue infarction or vascular injury. Prolonged fever also identifies patients at higher risk of a fatal outcome.

Age Factors↗