James W. Packwood

Tomographic mapping of human cerebral metabolism Visual stimulation and deprivation

Positron computed tomography was used to investigate changes in the local cerebral metabolic rate for glucose (LCMRGlc) of the visual cortex. Progressive increases in LCMRGlc were found from eyes-closed control to stimulation with white light, alternating black white checkerboard pattern, and a complex visual scene of a park, with the associative visual cortex increasing at a faster rate than the primary visual cortex as the visual scene complexity increased. A graded decrease in LCMRGlc of the visual cortex was found with a stepwise deletion of spontaneous cell firing at the retinal, geniculate and cortical level due to lesions. Lefthight metabolic symmetry of the visual cortex during monocular stimulation confirms 50% crossing of the human visual system. Neonatal blindness showed no apparent degeneration of the visual cortex and was equivalent to eyes-closed controls. The interictal state of a patient with visual seizures demonstrated a hypometabolic visual cortex with a 2.5-fold increase in metabolism during an ictal visual hallucination.

Evoked potentials predict the clinical changes in a multiple sclerosis drug study

Visual, brainstem auditory, and median nerve somatosensory evoked potential (EP) tests were performed annually during a 3-year, double-blind, placebo-controlled study of azathioprine with or without steroids in chronic progressive MS. Treatment-related visual and somatosensory EP changes became statistically different 1 year before corresponding differences were seen in the Standard Neurological Examination scores. The statistical significance of EP changes was substantially greater than seen for changes in other clinical scales. The degree of significance was increased by using EP latency values, rather than simple criteria for change. EPs are sensitive, objective measurements useful in MS therapeutic trials.

Asymptomatic HIV infection does not cause EEG abnormalities: Results from the Multicenter AIDS Cohort Study (MACS)*

We conducted EEG testing in 200 asymptomatic homosexual men, half of whom were HIV seropositive. We chose to include half of the subjects because they were rated as impaired on a neuropsychological screening test. We used both traditional visual EEG interpretation and quantitative EEG analysis. Abnormal EEGs and borderline degrees of EEG slowing occurred in 32% of these men. These EEG changes were not related to HIV serostatus. EEG changes did correlate with the impaired neuropsychological test performance. Clinicians faced with abnormal EEG results or borderline EEG slowing in an asymptomatic HIV-seropositive patient should not attribute the EEG change to effects of the serostatus itself but should look for other causes.

Somatosensory evoked potential monitoring with scalp and cervical recording

Publisher Summary This chapter explores the most common technique for spinal cord monitoring that uses somatosensory evoked potentials (SEPs) with stimulation at the ankles, and recording over the neck and the scalp. A similar technique is used for monitoring the intracranial lemniscal sensory system as it traverses the brainstem and cerebral hemispheres. For cervical or intracranial procedures, wrist stimulation often substitutes for or supplements the ankle stimulation techniques. The chapter reviews that monitoring provides services beyond simply warning of the complications. With monitoring, a surgeon can feel reassured about the spinal cord or lemniscal sensory pathway integrity and therefore, extend the surgical procedure to a greater degree than would have been done without monitoring. It discusses that patients and families can be reassured that certain feared complications are screened for during surgery. As such, monitoring provides an added dimension to surgical cases even when the SEP itself is unchanged throughout the procedure.

TOMOGRAPHIC MAPPING OF HUMAN CEREBRAL METABOLISM: VISUAL STIMULATION AND DEPRIVATION

Positron computed tomography was used to investigate changes in the local cerebral metabolic rate for glucose (LCMRGlc) of the visual cortex. Progressive increases in LCMRGlc were found from eyes-closed control to stimulation with white light, alternating black/white checkerboard pattern, and a complex visual scene of a park, with the associative visual cortex increasing at a faster rate than the primary visual cortex as the visual scene complexity increased. A graded decrease in LCMRGlc of the visual cortex was found with a stepwise deletion of spontaneous cell firing at the retinal, geniculate and cortical level due to lesions. Left/right metabolic symmetry of the visual cortex during monocular stimulation confirms 50% crossing of the human visual system. Neonatal blindness showed no apparent degeneration of the visual cortex and was equivalent to eyes-closed controls. The interictal state of a patient with visual seizures demonstrated a hypometabolic visual cortex with a 2.5-fold increase in metabolism during an ictal visual hallucination.