Biomedical subjects

V L Towle

Publications and source records attributed to V L Towle.

At least 19 recordsLinked to original sources

PubMed1998

Identification of the sensory/motor area and pathologic regions using ECoG coherence.

An electrophysiologic mapping technique which enables identification of the central sulcus and pathologic cortical regions is described. Electrocorticographic recordings of 1 min duration were recorded from 25 patients who were undergoing resection of tumors in the sensory-motor region or being evaluated for temporal lobectomy for epilepsy. Analysis of the patterns of subdural inter-electrode coherence revealed low coherence across the central sulcus for 11/12 cases where its location could be verified with direct cortical stimulation and/or somatosensory evoked potential mapping. Regions of high coherence identified the location of tumors in the sensory-motor region for 10/10 cases. Over the temporal lobe, localized areas of high coherence were evident in 8/9 epilepsy patients, but were not indicative of the location of mesial temporal lobe tumors or inter-ictal spiking, when present. We conclude that analysis of cortical coherence patterns may be helpful for revealing the location of pathologic processes relative to critical cortical areas.

Adolescent↗

PubMed1998

Auditory brain stem response in young and old guinea pigs.

OBJECTIVE: To characterize age-related auditory changes in genetically similar guinea pigs. BACKGROUND: In humans and animals, changes in hearing are known to occur with age. METHODS: Brain stem-evoked responses were measured in genetically similar guinea pigs that ranged 6-36 months in age. Changes in hearing and the input/output function curve were determined. RESULTS: Threshold shift with increase in age was seen. Marked reduction in amplitude of response with increasing age was also demonstrated. No change was seen in latency or interpeak interval. CONCLUSIONS: In genetically similar guinea pigs, age-related changes in threshold occurred. Latency and interpeak intervals remained unchanged. Amplitude of response decreased substantially after 12 months of age to a greater extent than predicted by threshold shifts alone. This phenomenon appears important in understanding the pathophysiology of age-related hearing loss.

Age Factors↗

PubMed1997

Intra-operative localization of sensorimotor cortex by cortical somatosensory evoked potentials: from analysis of waveforms to dipole source modeling.

Intra-operative localization of sensorimotor cortex is of increasing importance as neurosurgical techniques allow safe and accurate removal of lesions around the central sulcus. Although direct cortical recordings of somatosensory evoked potentials (SEPs) are known to be helpful for cortical localization, source localization models can provide more precise estimates than subjective visual analysis. In addition to intra-operative analysis of waveforms and amplitudes of SEPs to median nerve stimulation in 20 neurosurgical patients, we used a spatiotemporal dipole model to determine the location of the equivalent dipoles consistent with the cortical distribution of the SEPs. The early cortical SEPs were modeled by 2 equivalent dipoles located in the postcentral gyrus. The first dipole was primarily tangentially oriented and explained N20 and P20 peaks. The second dipole was primarily radially oriented and explained P25 activity. We found consistent localization of the first dipole in the postcentral gyrus, which was always located within 8 mm of the central sulcus, with an average distance of 3 mm. This finding provides an objective basis for using the SEP phase reversal method for cortical localization. We conclude that dipole source modeling of the cortical SEPs can be considered as an objective way of localizing the cortical hand sensory area.

Adolescent↗

PubMed1997

Maturation of human visual evoked potentials: 27 weeks conceptional age to 2 years.

Visual evoked potentials to pattern reversal and diffuse flash stimulation were recorded from 520 consecutive pediatric patients and 11 normal infants between the ages of 27 weeks post-conception and 24 months. The latency and peak-to-peak amplitude of the first reproducible positive peak of the binocular pattern visual evoked potential (P100) were measured for five check sizes subtending from 15' to 4 degrees of arc. Three developmental trends were noted: 1) a rapid increase in pattern resolution near term, 2) a subsequent decrease in the latency of P100, and 3) a gradual increase in the amplitude of P100. These three trends reflect the multiplicity of early maturation and are discussed in terms of changes in receptor growth and density, pathway myelination, and cortical synaptivity.

Age Factors↗

PubMed1997

Saccular influence on the otolith-spinal reflex and posture during sudden falls of the cat.

HYPOTHESIS: The saccule provides important input for the otolith spinal reflex during sudden falls in the cat. BACKGROUND: Previous studies on cats have identified two distinct components of muscle activity in response to sudden falls: an early otolith-dependent component (OSR) and a later nonlabyrinthine component associated with landing. The presence of an otolith-dependent reflex suggests a discrete role of the otolith organs in the control of posture and locomotion. METHODS: The influence of saccular input on the OSR during sudden falls was studied by simultaneous video and electromyographic (EMG) recordings obtained from saccular-deficient deaf white cats and white cats with normal hearing. RESULTS: A total of 628 sudden falls from five cats (two normal, one unilaterally deaf and two bilaterally deaf) were studied. Normal cats had a total of 337 drops, 276 of which (82%) were acceptable; a unilaterally deaf cat had a total of 79 drops, 56 of which (71%) were acceptable; deaf cats had a total of 212 drops, 177 of which (83%) were acceptable. The earliest of five observed behavioral events was that of forelimb extension which had a mean latency of 98 +/- 32 msec in normal cats and 139 +/- 28 msec in deaf cats (p < 0.0001). The mean latency of early EMG activity in normal cats was 19 +/- 7 msec and in deaf cats was 30 +/- 13 msec (p < 0.0001). The unilaterally deaf cat exhibited behavior and early EMG responses that were similar to those of normal cats. Deaf cats displayed poor body control during landings that improved with experience. CONCLUSIONS: These data demonstrate that the saccule provides important input for the otolith spinal reflex in the cat, and cats that lack both saccules have discernible behavioral and EMG differences in response to sudden falls, when compared with normal cats.

Animals↗

PubMed1996

Charles Bonnet syndrome: an early marker for dementia?

OBJECTIVE: To clarify the neuropsychological function in patients with Charles Bonnet Syndrome. DESIGN: Control group comparison study. SETTING: University of Chicago Hospitals. PARTICIPANTS: The neuropsychological function of 15 older adults with presenting complaints of visual hallucinations who met criteria for Charles Bonnet Syndrome (CBS) were compared with 11 demographically matched controls to determine if there was any evidence of functional brain impairment. CBS patients were screened for focal brain lesions and epileptic disturbance via MRI and EEG and also received pattern visual evoked potentials and ophthalmological examinations. MEASUREMENTS: Scores from the Wechsler Adult Intelligence Scale-Revised, Mattis Dementia Rating Scale, Wechsler Memory Scale, and the Auditory Verbal Learning Test were compared. RESULTS: Significant differences were found between the two groups on the neuropsychological measures. Moreover, 14 of 14 subjects had ocular abnormalities and six of eight had abnormal age-corrected pattern visual evoked potentials indicative of dysfunction in the visual system. CONCLUSIONS: The results of the study indicate that patients diagnosed with Charles Bonnet Syndrome evidence neuropsychological changes commonly associated with the early stages of dementia. Therefore, in patients with impaired vision, the appearance of cognitive deficits, albeit subtle, occur with the onset of visual hallucinations. We propose that isolated visual hallucinations in the older adult may be an indication of the early stages of dementia.

Aged↗

PubMed1996

Improved delayed visual reproduction test performance in multiple sclerosis patients receiving interferon beta-1b.

We assessed neuropsychological function longitudinally in 30 MS patients who participated in the pivotal trial of interferon beta-1b (IFN-beta-1b). Nine patients received high-dose IFN-beta-1b (8.0 million units), eight low-dose IFN-beta-1b (1.6 MIU), and 13 placebo. There was significant improvement in Wechsler Memory Scale Visual Reproduction-Delayed Recall scores between years 2 and 4 of the trial in MS subjects receiving high-dose IFN-beta-1b. Motoric performance, MRI lesion area, and depression rating scores did not correlate with this finding. Comparison of MRI at baseline and at years 2 and 4 revealed significant changes over time for the total cohort (p < 0.02). Mean lesion area in the high-dose group did not change over time, whereas the low-dose and placebo groups had increases in total lesion area of 28 and 36%, respectively, at year 4. Expanded disability status scale scores did not change significantly between years 2 and 4 of the trial, nor did they correlate with MRI lesion area at any assessment point. We conclude that high-dose IFN-beta-1b improves delayed visual reproduction test performance in MS patients, a finding unlikely to be explained by practice effects or brain lesion area.

Adult↗

PubMed1995

Displaying electrocorticographic findings on gyral anatomy.

Human electrocorticographic findings recorded from subdural arrays of electrodes were topographically mapped directly onto magnetic resonance images of gyral anatomy. With this technique gyri involved in generating somatosensory evoked potentials and epileptic phenomena are easily identified. Regions of the cortex which exhibit local spectral changes associated with cognitive tasks can also be visualized. These composite images of structure and function can provide insight regarding the functional organization of human cortex in relation to gyral anatomy and localized pathologic rhythms.

Brain Mapping↗

PubMed1995

Locating VEP equivalent dipoles in magnetic resonance images.

Pattern-reversal and diffuse flash visual evoked potentials (VEPs) were obtained from 4 normal adults. A spatiotemporal dipole model was used to determine the location of the hypothetical equivalent dipoles consistent with the scalp distribution of the VEPs. Equivalent dipoles representing ERG and VEP activity were placed within 3-D magnetic resonance images of the brain. Most of the localization error appeared to be due to inadequate sampling of the potential field in frontal and occipital areas by the 10-20 system of electrode placement. Locating electrophysiologic dipoles within magnetic resonance images of brain structure allows evaluation of dipole localization techniques.

Adult↗

PubMed1994

Functional magnetic resonance studies of the reorganization of the human hand sensorimotor area after unilateral brain injury in the perinatal period.

Functional magnetic resonance imaging was used to map the hand sensorimotor area of hemiparetic adolescents and young adults who had suffered unilateral brain damage in the perinatal period. Unlike normal subjects, who exhibit cortical activation primarily contralateral to voluntary finger movements, the hemiparetic patients' intact hemispheres were equally activated by contralateral and ipsilateral finger movements. Our findings are consistent with previous clinical observations and animal experiments which suggest that the immature brain is able to reorganize in response to focal injury.

Adolescent↗

PubMed1993

The spatial location of EEG electrodes: locating the best-fitting sphere relative to cortical anatomy.

The location of the international 10-20 system electrode positions and 14 fiducial landmarks are described in cartesian coordinates (+/- 1.4 mm average accuracy). Six replications were obtained on 3 separate days from 4 normal subjects, who were compared to each other with a best-fit sphere algorithm. Test-retest reliability depended on the electrode position: the parasagittal electrodes were associated with greater measurement errors (maximum 7 mm) than midline locations. Location variability due to head shape was greatest in the temporal region, averaging 5 mm from the mean. For each subject's electrode locations a best-fitting sphere was determined (79-87 mm radius, 6% average error). A surface-fitting algorithm was used to transfer the electrode locations and best-fitting sphere to MR images of the brain and scalp. The center of the best-fitting sphere coincided with the floor of the third ventricle 5 mm anterior to the posterior commissure. The melding of EEG electrode location information with brain anatomy provides an empirical basis for associating hypothetical equivalent dipole locations with their anatomical substrates.

Adult↗

PubMed1992

Hypoglycemic thresholds for cognitive dysfunction in IDDM.

Fourteen poorly controlled insulin-dependent diabetes mellitus (IDDM) patients (HbA1c 11 +/- 0.5%) with a mean +/- SE duration of disease of 15 +/- 2 yr were studied to evaluate the hypoglycemic threshold for cognitive dysfunction under insulin-induced hypoglycemia. The P300 event-related potential, a measure of cognitive function, and reaction time (RT) in response to visual stimuli under euglycemic conditions and at plasma glucose concentrations of 3.5 and 2.5 mM (63 and 45 mg/dl, respectively) during a constant insulin infusion were recorded. Baseline P300 latency was similar to that of a nondiabetic control group, but baseline RT was greater in the IDDM group. There was no increase in P300 latency or RT under euglycemic clamp conditions or at a plasma glucose level of 3.5 mM (63 mg/dl). However, when plasma glucose was lowered to 2.5 mM (45 mg/dl), there was an increase in P300 latency and a prolongation of RT. As plasma glucose returned to baseline, P300 latency and RT remained prolonged. After administration of intravenous glucose and a meal, P300 latency and RT returned to baseline. P140, an event-related potential reflecting sensory processes, was not altered. Because P300 latency changes paralleled RT changes, hypoglycemia appears to slow decision-making processes in IDDM. This study revealed that 1) baseline P300 latency is not elevated in poorly controlled IDDM patients, suggesting no cumulative cognitive dysfunction.

Blood Glucose↗

PubMed1990

Hypoglycemic thresholds for cognitive dysfunction in humans.

Nineteen healthy adult volunteers were studied to define the nature of and threshold for the cognitive dysfunction that occurs during insulin-induced hypoglycemia. The P300 cerebral event-related potential is an electrophysiological correlate of cognitive decision-making processes that can be measured in response to either an auditory or visual stimulus. P300 and reaction time (RT) were recorded from a visual stimulus under euglycemic conditions and at plasma glucose concentrations of 3.3 and 2.6 mM during insulin infusion in 10 subjects. Reducing plasma glucose levels to 3.3 mM was not associated with an increase in either the latency or amplitude of the P300 component or a change in RT. However, further lowering of plasma glucose to 2.6 mM resulted in an increase in the latency of P300 and a prolongation in RT. Similar changes were seen for the auditory P300 in experiments performed on 9 additional subjects in which both auditory and visual stimuli were presented. The prolongation of P300 did not correct immediately when plasma glucose was raised to basal levels with intravenous glucose but returned to normal 45-75 min later, after ingestion of a carbohydrate-containing meal. Analysis of another event-related potential, P140 (a measure of the sensory processes), showed no change in response to hypoglycemia. Prolongation of RT paralleled the prolongation of P300 latency, suggesting that motor processes were not altered. Therefore, hypoglycemia appears to induce abnormalities in decision-making processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Hemi-field pattern visual evoked potentials: a comparison of display and analysis techniques.

Three methods for analyzing the spatial organization of visual evoked potentials were compared. Pattern reversal visual evoked potentials were obtained from a single subject under three viewing conditions: stimulation of the left, right, and both visual fields. The scalp distribution of the VEP to 1 deg checks was displayed using three recording and analysis techniques: a conventional horizontal occipital array of electrodes, topographic mapping, and 3-dimensional evoked potentials. All three techniques revealed "paradoxical" lateralization of P100. The relative merits of each technique are discussed.

Brain Mapping↗

PubMed1989

Electrophysiologic studies on locked-in patients: heterogeneity of findings.

Somatosensory evoked potentials, brain-stem auditory evoked potentials and electroencephalograms were obtained from 9 patients with the diagnosis of 'locked-in' syndrome. No pattern of evoked potential abnormality was specific to this syndrome, with findings ranging from bilaterally normal to unilaterally or bilaterally absent. The evoked potential studies complemented radiographic findings in defining the extent of the lesion and revealed that a portion of the pontine tegmentum was usually involved. Pathology from 2 patients corroborated the findings of the evoked potential studies. The value of evoked potential studies of patients with locked-in syndrome is to provide early objective evidence of brain-stem involvement independent of the clinical examination, EEG and radiographic studies.

Adult↗

PubMed1989

Vector analysis of three-dimensional evoked potentials: eccentric dipoles.

The quantitative description of three-dimensional cerebral evoked potentials is extended to include eccentric dipolar sources. Eccentricity-related distortions in dipole orientation and magnitude are assessed. The use of nonstandard montages, the prediction of topographic surface maps, dynamic analysis, and theoretical mechanisms of planar segment formation are discussed.

Brain↗

PubMed1986

Clinical studies with an aldose reductase inhibitor in the autonomic and somatic neuropathies of diabetes.

Clinical investigations with the aldose reductase inhibitor (ARI) sorbinil in diabetic patients with neuropathy are described. Cardiac autonomic neuropathy was studied in 36 patients, in a double-blind, placebo-controlled, randomized, noncrossover trial. Patients received sorbinil (250 mg qd) or placebo over 6 weeks after a one-week baseline period. Diabetic control did not change over the study period, as indicated by unchanged glycohemoglobin. Response was assessed by expiration/inspiration (E/I) ratios on EKG during 6 c/min respiration and resting minimum heart rate, both measures of vagal function. In the sorbinil group, E/I ratios improved from 1.074 +/- 0.012 to 1.096 +/- 0.020 (P less than 0.03) with a slight decrease in the placebo group from 1.112 +/- 0.023 to 1.105 +/- 0.023 (P = NS). The difference between the week 6 and week 0 changes in each group was significant (P less than 0.01). Resting minimum heart rate decreased in the sorbinil group from 76.4 +/- 2.3 to 66.8 +/- 2.4 beats/min (P less than 0.001), with a mean change of 10 +/- 2. In the placebo group, heart rate was unchanged (77.9 +/- 3.9 to 77.5 +/- 3.3). The two sample t tests of the within-group differences were likewise significant (P less than 0.001). These changes in both E/I ratio and resting minimum heart rate are consistent with a sorbinil-related improvement in cardiac parasympathetic nerve function. Several isolated cases with apparent sorbinil-related improvement in autonomic symptoms will also be described. Studies of somatic neuropathy have previously shown improvement in nerve conduction velocities with sorbinil. In a study of 11 patients with severely painful diabetic neuropathy treated with sorbinil for 3 weeks [placebo-controlled in single-blind fashion (n = 8)], pains (as assessed on a 0 to 20 rating scale) improved from a mean score of 16 down to 8, with deterioration following drug withdrawal. Objective improvements in sensation and strength were observed in some cases. In this group of patients, statistically significant improvements in nerve conduction velocity, E/I ratios, and resting minimal heart rate, similar to those previously discussed, were also documented. Somatosensory-evoked potentials studies in the 36-patient study showed significant improvements in peripheral conduction and cortical responses. Sorbinil toxicity in 106 patients was 11.3%, with sex incidence of 7/73 males (9.6%) and 5/33 females (15.2%).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1986

Spectral analysis of EEG during carotid endarterectomy.

Spectral analysis of the electroencephalogram (EEG) was monitored during 105 carotid endarterectomies. Seventy-eight percent of the patients showed no significant change in EEG spectral power as a result of clamping of the internal carotid artery. Two patterns of change were observed in the remaining 22% of patients: partial reduction (significant decrease of power in one or two of three frequency bands) and global reduction (significant decrease of power in all three frequency bands). High frequencies (over 10.5 Hz) changed more frequently with clamping than did low frequencies (less than 6 Hz), but reduction of high frequencies alone was tolerated with no postoperative deficits. The only non-shunted patient demonstrating global EEG reduction for the duration of carotid clamping suffered a transient hemiparesis.

Aged↗