Biomedical subjects

N Bleich

Publications and source records attributed to N Bleich.

22 records · Page 2Linked to original sources

PubMed1985

Three-channel Lissajous' trajectory of human auditory brain-stem evoked potentials. I. Normative measures.

Three-channel Lissajous' trajectories (3-CLTs) of auditory brainstem evoked potentials (ABEPs) were obtained from 14 humans (28 ears) in response to 75 dB nHL, 10/sec alternating polarity clicks. A normative set of 3-CLT quantitative measures was calculated and compared with amplitudes and latencies of the simultaneously recorded, single-channel, vertex-mastoid ABEP. The comparison included average values as well as intersubject variability. The 3-CLT measures included: apex latencies; planar segment durations, orientation, size and shape; trajectory-amplitude peaks and their latencies. Apex latencies of 3-CLT were comparable to peak latencies of the vertex-mastoid records, both in absolute values and in intersubject variability. Durations of planar segments were approximately 0.7 msec and their standard deviations were about a half of their average. Individual planar segment orientations were typically within 50 degrees of the normative average. Trajectory amplitudes were, in general, somewhat larger than peak amplitudes of the vertex-mastoid records, while their intersubject variabilities were comparable. Size and shape measures of planar segments were variable across subjects, making their clinical use, in their present form, questionable. The quantitative study of the 3-CLT of auditory brain-stem evoked potentials will enable evaluation of normal, as well as pathological, evoked potentials, to further the understanding and utility of this comprehensive representation of brain-stem function.

Adult↗

PubMed1982

Auditory brain stem potentials evoked by clicks in notch-filtered masking noise.

Auditory brain stem evoked potentials (ABEPs) were recorded in response to wide-band clicks in notch-filtered masking noise. Notches (1/2 octave wide, 96 dB/octave slopes) were centered on the audiometric frequencies. Without the notches, masking noise intensity was adjusted to obliterate ABEPs. Intensity series, with both clicks and masking noise attenuated by the same 10 dB steps, were obtained for clicks masked by notched noise, in addition to unmasked clicks. Absolute latencies and interpeak latency differences of ABEPs to clicks in notched noise did not change with notch frequency. Absolute latencies were longer for ABEPs to clicks with notched noise than to unmasked clicks. For all stimuli, latencies were prolonged when stimulus intensity decreased. The findings suggest that ABEPs to clicks in notched noise are initiated by low threshold cochlear activation which may account for the independence of component latency from 'travelling wave' propagation time. These potentials may be representative of only one subset of the constituents of ABEPs to wide-bank unmasked clicks. The clinical application of these potentials must await elucidation of their relevance to the process of hearing.

Acoustic Stimulation↗

PubMed1982

Short latency visual evoked potentials in man.

Contrary to auditory and somatosensory evoked potentials, surface recorded visual evoked potentials which arise in subcortical neural elements have rarely been described. Considerable disagreement exists between the reports in the literature on such visual potentials. In this study, flash stimuli were used to evoke the potentials which were recorded from the skin overlying the infra-orbital ridge, outer canthus, middle of the forehead, vertex, mastoid ipsilateral to the stimulated eye and inion, using a non-cephalic reference. The potentials were amplified in a band which was chosen to omit slow retinal and cortical potentials, and to enhance activity which might include compound neural activity. Potentials were recorded from 9 subjects (13 eyes), and for each one the effects of eye position and stimulus intensity were studied. The results indicate that the series of components recorded within the first 100 msec following photic stimulation were volume-conducted activity generated by a subset of the visual system which is activated by luminosity changes. The generators of the first 4 or 5 components seem to be situated within the retina, the subsequent components seem to be generated in the optic nerve or tracts, and the later components may be thalamo-cortical in origin. These potentials may complement pattern evoked potentials in a more accurate definition of sites of lesions along the visual pathway.

Adult↗

PubMedDate not supplied

The effects of digital filtering on feline auditory brain-stem evoked potentials.

The power spectrum of the feline auditory brain-stem evoked potentials (ABEPs) consists of 3 frequency bands, similar to the human wave form, but differing in range. The frequency bands in the feline spectra were separated by notches at 326 Hz and 732 Hz. Click-evoked ABEP from 15 cats were digitally filtered in 3 passbands: (1) below 326 Hz ('slow filter'), (2) between 326 and 732 Hz ('medium filter'); and (3) between 732 and 1790 Hz ('fast filter'). Filtering in each of these bands differentially affected the ABEP components. The vertex positive components are labeled by their order of appearance, i.e., 1, 2, ... 5. Peak 1 is subdivided into 2 subcomponents labeled 1a and 1b. The slow filter was associated with the loss of all components leaving a slow potential shift, i.e., the 'pedestal' peaking at the latency of peak 4. The medium filter was associated with the loss of components 1a, 1b and 2, sparing 3 and 4. The fast filter was associated with the loss of 1b and a diminution of 2. Comparing cat and human ABEP, feline components 2, 3 and 4 behaved precisely the same as the human II, III and V. In contrast to the human I, the feline first component (1a) was not detected with the medium filter. No feline component, following peak 1 in the unfiltered wave form, disappeared with the slow and medium filters, and reemerged with the fast filter (as human IV does).(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗