Biomedical subjects

V L Towle

Publications and source records attributed to V L Towle.

39 records · Page 3Linked to original sources

PubMedDate not supplied

Three-dimensional human pattern visual evoked potentials. I. Normal subjects.

Pattern visual evoked potentials (PVEPs) were obtained from 30 normal adult volunteers, recording from both a conventional horizontal occipital array and three orthogonal bipolar antipodal channels approximating the three dimensions of space. Central and eccentric fixation of 60' checks and central fixation of 30' checks under binocular and monocular viewing conditions was employed. The three antipodal wave forms were displayed as a single 3-D Lissajous trajectory which contained four apices, corresponding to P40 (apex A), N70 (apex B), P100 (apex C) and N125 (apex D). The 3-D evoked potentials depicted the dynamic nature of the human PVEP in terms of changes in the 3-D voltage-voltage-voltage plots of the recordings. The orientation of the A-B, B-C and C-D curvilinear segments reflected the stimulating condition (central fixation vs. right vs. left hemi-field stimulation) for all subjects with more accuracy than did the wave forms from the conventional array. Spherical statistical methods are described for quantifying and evaluating 3-D evoked potential recordings.

Adult↗

PubMedDate not supplied

Three-dimensional human pattern visual evoked potentials. II. Multiple sclerosis patients.

Pattern visual evoked potentials were obtained from 46 patients with definite relapsing/remitting multiple sclerosis, using both a conventional 5-channel occipital array and a 3-D recording technique consisting of three bipolar derivations approximating the three dimensions of space. These three orthogonal wave forms were displayed as a 3-D Lissajous trajectory for each subject. Two of the 15 patients with completely normal conventional pattern VEPs had abnormalities of the orientation of the B-C curvilinear segment of the 3-D pattern VEPs. Delays in the first major occipital positive component (P100) were evident using both techniques; the correlation between P100 latency and the latency of the corresponding trajectory apex was r = 0.99 (P less than 0.01). Post-chiasmal MRI abnormalities were associated with 3-D VEP orientation abnormalities. Three-dimensional pattern VEPs are moderately more sensitive than conventional pattern VEPs at detecting dysfunction posterior to the optic chiasm in demyelinating disease and do not require the use of eccentric fixation to do so.

Adult↗

PubMedDate not supplied

Tetrahedral recording of 3-D BAEPs: evidence for the centered dipole model.

Three-dimensional brain-stem auditory evoked potentials (3-D BAEPs) were recorded from 12 normal subjects using a new tetrahedral montage, as well as two other bipolar montages previously described for 3-channel Lissajous' trajectories (3-CLTs). Mean responses, as well as between-subject and within-subject variability were described. A mathematical transformation was applied to the recorded trajectories to render them in a common canonical form to test the assumption that the BAEP conforms to a centrally generated dipolar field. Apex, segment, and plane orientations were measured for each trajectory, and discrepancies between montages were evaluated to judge the adequacy of the centered dipole model. For the vector means of apices, segments, and planes, median angles of discrepancy between montages ranged from 10 to 23 degrees. These results support the validity of a centered dipole model for the BAEP and affirm the rationale for employing the 3-channel recording technique. Among the montages studied, the tetrahedron provided maximum economy by using fewer electrodes, avoided certain problematic recording sites, and produced less variable data.

Acoustic Stimulation↗