James J. Stockard

Clinical and pathologic correlates of brain stem auditory response abnormalities

Short-latency auditory evoked responses were recorded in over 100 neurologic patients. Abnormalities of each response component were correlated with postmortem or radiologic localization of different brain stem lesions. These findings suggested that waves I-VII largely reflect activity at the following levels of the auditory pathway: acoustic nerve (I), pontomedullary junction (II), caudal pons (Ill), rostral pons or midbrain (IV), midbrain (V), thalamus (VI), and thalamus or auditory radiation (VII). When this information was applied prospectively to the evaluation of brain stem dysfunction, response abnormalities proved useful in detecting and localizing certain lesions not revealed by other tests. Serial recordings provided information about the evolution of brain stem lesions and their response to therapy.

Hypotension-Induced Changes in Cerebral Function During Cardiac Surgery

In a series of 75 patients undergoing cardiac operations with the assistance of cardiopulmonary bypass (CPB), 15 patients were subjected to relatively large hypotensive stresses during CPB as measured by the depth and duration of the fall in cerebral perfusion pressure. Of these 15 patients, eight manifested cerebral dysfunction postoperatively ranging from temporary exacerbation of pre-existing focal neurological deficits to irreversible coma. In each of these eight cases, EEG disturbances which first appeared at the time of hypotensive episodes during CPB persisted postoperatively and correlated with the nature and evolution of the clinical deficit. In two of the patients who did not regain consciousness postoperatively, neuropathological studies revealed bilateral laminar cortical necrosis, primarily involving cerebral cortex in one case and cerebellar cortex in the other, with accentuation in arterial border zones. Of seven other patients who suffered comparable exposures to hypotension during CPB, none evidenced cerebral dysfunction postoperatively. The most important determinants of this selective vulnerability to low extracorporeal perfusion pressure appeared to be the “reperfusion” pressure established after the hypotensive episode, postoperative blood pressure and cardiac output, and brain temperature at the time of the hypotension. Advanced age and history of cerebrovascular insufficiency were the greatest risk factors among patient variables.

Auditory brain stem response variability in infants.

Variations in auditory brain stem response latency, threshold, and amplitude ratio were related to stimulus, recording, subject, and pathologic factors in normal and high-risk infants.

Clinically useful applications of evoked potentials in adult neurology.

Summary Recent advances in the field of sensory evoked potentials (EPs) have allowed assessment of function in regions of the nervous system that were previously inaccessible to noninvasive electrophysiologic study. Pattern visual and brainstem auditory EPs, respectively, are more sensitive to certain optic nerve or posterior fossa lesions than either clinical or laboratory tests. Short-latency somatosensory EPs from the upper and lower extermities are sensitive to pathollogy at cervicomedullary and thoracolumbar levels of the neuraxis as well as to suprasegmental lesions. This article reviews the development of these as clinically useful tools and the applications in which they have contributed most to the practice of adult neurology.

Effects of Acute and Chronic Paleocerebellar Stimulation on Experimental Models of Epilepsy in the Cat: Studies with Enflurane, Pentylenetetrazol, Penicillin, and Chloralose

Effects of acute and chronic paleocerebellar stimulation were evaluated in four experimental models of epilepsy in 24 adult cats chronically implanted with bilaterally symmetric parasagittal electrocorticographic electrodes and anterior lobe cerebellar stimulation electrodes. Pentylenetetrazol was given intraveneously in 50‐mg increments or 4% enflurane was inspired until grand mal seizures occurred spontaneously or were triggered by photic or auditory stimuli. Alpha‐chloralose, 50 mg/kg, was injected intraperitoneally to produce a model of stimulus‐sensitive myoclonus and sodium penicillin G, 350,000 units/kg, was injected intramuscularly to produce a model of petit mal epilepsy. One‐ to 250‐Hz electrical stimulation of paleocerebellar cortical surfaces was performed with constant‐voltage or constant‐current stimulators at threshold and suprathreshold intensities with average intensities of 8 V and 2.5 mA, respectively. Acute or chronic, threshold or suprathreshold paleocerebellar stimulation did not predictably alter the electrographic or clinical manifestations in any of these four models.

Neurologic and electroencephalographic correlates in glutethimide intoxication

Neurologic and electroencephalographic (EEG) examinations were performed every two hours during a case of severe glutethimide intoxication resulting from the acute ingestion of at least 15 grams of glutethimide. Neurologic data were reduced to 10 measurements of brainstem function and plotted as an index that varied cyclically in amplitude during the clinical course. Electroencephalographic data were computer‐processed by power spectral methods and related to the brainstem function index. Good positive correlation existed between the frequency and reactivity of EEG activity and the level of brainstem function as reflected in the index. The cyclic and, sometimes, unilateral nature of the clinical findings previously reported in glutethimide coma was confirmed and seen to be reflected in the EEG. The present case also indicates that, in the absence of cerebral ischemia or hypoxemia secondary to cardiopulmonary depression, complete clinical recovery from glutethimide‐induced coma is possible no matter how severe the presenting neurologic and EEG signs.

Cross-Sectional and Longitudinal Studies of Brain Stem Auditory-Evoked Potentials in High-Risk Infants

This chapter reviews the use of brainstem auditory-evoked potentials (BAEPs) as a diagnostic tool and prognostic indicator in infants at risk for otoneurological impairment in the first year of life. As a diagnostic tool, BAEPs can provide information about the presence, nature, location, and degree of dysfunction in the developing auditory nervous system. When performed serially (longitudinally), the test can answer prognostic questions such as whether the diagnosed otoneurological dysfunction is chronic vs. transient or static vs. evolving and, if evolving, whether it is progressive or resolving. Serial BAEP studies also allow monitoring of the efficacy of any therapeutic interventions.