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R M Harper

Publications and source records attributed to R M Harper.

183 records · Page 11Linked to original sources
PubMedDate not supplied

MR imaging signal response to sustained stimulation in human visual cortex.

The response of signal intensity to transient (on-off) motor and sensory stimulation has been well studied; however, the dependence of signal response on the duration of stimulus requires further characterization. The objective of this study was to determine the time course of signal response in the human visual cortex to prolonged, sustained stimulation and to examine possible contributory physiologic mechanisms. Nine healthy volunteers underwent magnetic resonance (MR) imaging during sustained visual stimulation with light-proof binocular goggles. With photic stimulation, activation was observed in all subjects as an increase in signal intensity of the visual cortex. With sustained stimulation, a gradual decrease in signal intensity was subsequently observed, with progression toward an apparent steady state. Correlation with positron emission tomographic, MR spectroscopic, and visual evoked-potential data suggests that the initial uncoupling of cerebral blood flow and oxidative metabolism with a neuronal activation burst may represent a transient phenomenon. This quick-response phase may proceed to an equilibrium coupling of flow and oxidative metabolism, with a gradual normalization of venous deoxyhemoglobin levels and signal intensity.

Adult↗
PubMedDate not supplied

Cardiac and respiratory correlations with unit discharge in epileptic human temporal lobe.

We recorded respiratory activity and electrocardiogram (ECG) together with single cell activity from the amygdala and hippocampus of epileptic patients who later received anterotemporal lobectomy. Cross-correlation histograms were used to test for neuronal discharge timing relationships with inspiration or ECG. Linear regression was used to test for correlations of inspiratory time, respiratory period, and heart rate (HR) with tonic unit rate for each breath. Of 129 cells from 16 patients who later had resection, 89 were contralateral and 40 were ipsilateral to the resected lobe. Of the contralateral cells, 19% had a timing relationship with the cardiac cycle and only 1% had such a relationship with the respiratory cycle. Tonic correlations with HR were noted in 22% and with respiratory period and inspiratory time in 11 and 6%. Neither these percentages nor mean discharge rate differed between structures, although variance in rate was much higher on the resected side. Amygdala cells on the resected side showed more correlations with the cardiac cycle (55 vs. 20%), respiratory period (46 vs. 3%), and inspiratory time (27 vs. 7%) and were more likely to show several types of correlation. The results suggest a selective loss of ipsilateral amygdala cells and/or afferents, favoring relationships with cardiac- and respiratory-related systems and a possible synaptic reorganization of remaining cardiorespiratory afferents.

Cardiovascular System↗