Auditory P300 abnormalities and leukocyte activation in HIV infection.

To evaluate whether P300 testing might serve as a screening modality for the early detection of HIV-related neuropathology, we tested 26 HIV-infected men (23 without neurologic symptoms, 2 with peripheral neuropathy, 1 with AIDS-associated dementia) and 15 controls. Although they had no overt neurologic symptoms, the P300 latency was delayed or undetectable in 30% of patients without clinically evident neurologic disease. P300 latencies did not correlate with peripheral blood CD4 T-cell count, serum quinolinic acid or p24 antigen levels, or the numbers of activated peripheral blood monocytes. Three individuals with abnormal P300 latencies had been HIV-seropositive for < or = 1 year, suggesting that delayed evoked responses detect early neurologic dysfunction. P300 responses do not predict imminent dementia. In only one previously asymptomatic individual with abnormal P300 waveforms have overt neurologic symptoms developed during a 2-year followup. Extended longitudinal studies will be necessary to define the predictive value of P300 latencies in the development of AIDS-related dementia. However, the sensitivity, quantitative nature, and speed of administration of this test suggest that it may be useful for identification of early neurologic involvement in HIV infection.

Speech-spectrum analysis of Mandarin: implications for hearing-aid fittings in a multi-ethnic society.

Using similar recording and analysis techniques, the long-term average speech spectra of English and Mandarin were compared in order to identify difference that might influence hearing-aid fitting strategies. Despite the well-documented pitch contour differences between English and Mandarin, no significant difference was found in the long-term average spectral analysis. Implications for hearing-aid prescription are discussed.

Asymmetries in topographic brain maps of auditory evoked potentials in the elderly.

We compared topographic brain maps of the middle response (MR) and late response (LR) auditory evoked potentials in two groups of elderly males. Subjects were categorized on the basis of the performance of the poorer hearing ear on the Synthetic Sentence Identification (SSI) test. Evoked potentials, obtained in response to 1000-Hz tone pips and tone bursts, were recorded under three conditions of sound stimulation:binaural (BIN), left ear only (LE), and right ear only (RE). Comparisons of the topographic brain maps generated by the two groups revealed significant asymmetry in the MR of the experimental group. LE stimulation produced a larger response over the right hemisphere, and RE stimulation produced a larger response over the left hemisphere. This asymmetry was not observed in the experimental group with binaural stimulation, or in the control group in any of the three stimulation conditions. An analogous asymmetry was not recognized in the LR in either group for any of the three sound conditions. Results are interpreted in relation to the recently proposed model of multiple middle latency generators.

Case studies in binaural interference: converging evidence from behavioral and electrophysiologic measures.

We present four case reports of elderly hearing-impaired persons demonstrating a binaural interference effect. Performance measures were poorer when stimulation was binaural than when it was monaural. In the first case the effect is shown for aided speech recognition scores. In the second case it is shown in topographic brain maps of the middle-latency auditory evoked potential. In the third and fourth cases it is shown for both aided speech recognition and the middle-latency response. The effect may be analogous to the phenomenon of binocular rivalry in the visual domain.

Effect of handedness on the middle latency auditory evoked potential.

The effect of handedness on the middle latency response of the auditory evoked potential was investigated by testing 16 right-handed and 16 left-handed young adults with normal hearing. Each handedness group contained eight males and eight females. Peaks PO, N(a),P(a),Nb,and Pb showed a progressive, statistically significant latency increase in left-handed subjects when compared with right-handed subjects. The latency difference was 1.1 ms at peak P(a) and 3.6 ms at peak Pb. There was no significant latency difference between males and females. Topographic brain mapping showed that the distribution of positivity of wave Pb was similar to the distribution for wave P(a) in both right- and left-handed subjects.

Test-retest reliability of combined sensory index: implications for diagnosing carpal tunnel syndrome.

When compared to single nerve conduction tests, the combined sensory index (CSI) has been shown previously to have superior sensitivity and specificity for diagnosing carpal tunnel syndrome. The CSI is the sum of (1) median-ulnar ring finger antidromic latency difference at 14 cm (ring-diff); (2) median-radial thumb antidromic latency difference at 10 cm (thumb-diff); and (3) median-ulnar midpalmar orthodromic latency difference at 8 cm (palm-diff). To evaluate the reliability of single nerve conduction tests (ring-diff, thumb-diff, and palm-diff) vs. a combined summary variable (CSI), we conducted a prospective study during which the same investigator performed test and retest sessions on one hand of 32 subjects. Results showed that the CSI had the highest test-retest reliability (Spearman rho = 0.95), when compared with ring-diff, thumb-diff, and palm-diff (Spearman rho = 0.67, 0.75, and 0.74, respectively). Therefore, we propose the use of the CSI as not only an accurate but also a reliable method for diagnosing carpal tunnel syndrome.

Comparison of speech-evoked v tone-evoked P300 response: implications for predicting outcomes in patients with traumatic brain injury.

The P300 response is a cognitive event-related potential recorded over the scalp. The tone-evoked P300 response has been used to predict outcomes of patients with brain injury. However, it may lead to false predictions because some normal people have a very small tone-evoked P300 response. It is hypothesized that speech may generate a more robust P300 response than tones. A voice-generator prototype was designed for this study. The rare speech signal was the word "mommy" in a female voice. The common signal was a 1000-Hz tone. Twenty-two normal adults (11 males, 11 females; age range, 18-60 yr) were tested for both speech-evoked and tone-evoked P300 responses. Speech-evoked P300 responses had significantly larger amplitudes (mean, 12.1 microV) than the tone-evoked responses (mean, 5.9 microV; P < 0.0001). Six subjects with brain injury were also tested using the same protocol: two subjects with severe brain injury showed no response to either stimulus. Both died within 1 wk after the testing. Although two subjects with moderate brain injury could not complete the testing because of agitated behavior, two other subjects with mild traumatic brain injury showed a larger speech-evoked than tone-evoked P300 response. The speech-evoked P300 response may be promising in predicting outcomes of patients with brain injury.

Vastus medialis obliquus and vastus lateralis activity in open and closed kinetic chain exercises in patients with patellofemoral pain syndrome: an electromyographic study.

OBJECTIVES: To evaluate the electromyographic activities of vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles in open and closed kinetic chain exercises in subjects with patellofemoral pain syndrome (PFPS). DESIGN: Case-controlled study. SETTING: Rehabilitation science center in a tertiary medical center. PARTICIPANTS: Ten patients with bilateral knee pain diagnosed with PFPS and 10 healthy volunteers. INTERVENTIONS: Subjects performed open kinetic chain exercise on an isokinetic dynamometer and closed kinetic chain exercise by squat-to-stand and stand-to-squat tasks. Surface electromyography was done for the VMO and VL muscles. MAIN OUTCOME MEASURES: VMO/VL ratios were calculated after normalization of muscle activities. RESULTS: The VMO/VL ratios of PFPS subjects were significantly lower than were those of unimpaired subjects during knee isokinetic closed kinetic chain exercises (p = .047). However, there was no statistical difference in VMO/VL ratio between subjects with and without PFPS during closed kinetic chain exercises (p = .623). Maximum VMO/VL ratio was obtained at 60 degrees knee flexion in closed kinetic chain exercise. CONCLUSION: In closed kinetic chain exercises, more selective VMO activation can be obtained at 60 degrees knee flexion. Maximal VMO/VL ratio was observed at this knee flexion angle, and muscle contraction intensity was also greatest.