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Alan H Lockwood

Publications and source records attributed to Alan H Lockwood.

8 recordsLinked to original sources
PubMed2002

Tinnitus.

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Algorithms↗
PubMed2002

Brain imaging of the effects of lidocaine on tinnitus.

Using a single-blind placebo-controlled design, we mapped lidocaine related changes in neural activity, measured by regional cerebral blood flow (rCBF) with (15)O-H(2)O positron emission tomography. Intravenous lidocaine produced both increases and decreases in the loudness of tinnitus. The change in tinnitus loudness was associated with a statistically significant change in neural activity in the right temporal lobe in auditory association cortex. Decreases in tinnitus loudness resulted in larger changes in rCBF than increases. The unilateral activation pattern associated with tinnitus, in contrast with the bilateral activation produced by a real sound, suggests that tinnitus originates in the central auditory system rather than the cochlea. In addition, generalized lidocaine effects were found in the basal ganglia, thalamus, and a region spanning the Rolandic fissure.

Acoustic Stimulation↗
PubMed2002

Hepatic encephalopathy.

Many patients with cirrhosis of the liver who appear to be overtly normal, using standard bedside examination techniques, test in the impaired range on one or more neuropsychological tests. These impairments affect the quality of life. Improvement in affected cognitive domains and the quality of life may follow the institution of treatment.

Brain↗
PubMed2002

Correlations between cerebral glucose metabolism and neuropsychological test performance in nonalcoholic cirrhotics.

Many cirrhotics have abnormal neuropsychological test scores. To define the anatomical-physiological basis for encephalopathy in nonalcoholic cirrhotics, we performed resting-state fluorodeoxyglucose positron emission tomographic scans and administered a neuropsychological test battery to 18 patients and 10 controls. Statistical parametric mapping correlated changes in regional glucose metabolism with performance on the individual tests and a composite battery score. In patients without overt encephalopathy, poor performance correlated with reductions in metabolism in the anterior cingulate. In all patients, poor performance on the battery was positively correlated (p < 0.001) with glucose metabolism in bifrontal and biparietal regions of the cerebral cortex and negatively correlated with metabolism in hippocampal, lingual, and fusiform gyri and the posterior putamen. Similar patterns of abnormal metabolism were found when comparing the patients to 10 controls. Metabolic abnormalities in the anterior attention system and association cortices mediating executive and integrative function form the pathophysiological basis for mild hepatic encephalopathy.

Aged↗
PubMed2002

Positron emission tomography in the study of hepatic encephalopathy.

Positron emission tomography (PET) is a powerful and versatile tool for the investigation of hepatic encephalopathy (HE). This nuclear medicine imaging technique produces quantitative images of the distribution of a radiopharmaceutical at one or more times after its administration. Thus, PET images can be used as data in mathematical models of physiologically important processes, including cerebral blood flow, an index of neural activity, or glucose and ammonia metabolism. Using PET, we have demonstrated abnormalities in all of these processes in patients, even though many had only minimal HE. In HE patients we have found increases in the cerebral ammonia metabolic rate, because of hyperammonemia and an increase in the permeability of the blood-brain barrier to ammonia and abnormal patterns of blood flow and glucose metabolism. In a recent collaborative study, alterations in the resting glucose metabolic rate were found to have significant correlations with a variety of neuropsychological tests used to detect mild HE including Trailmaking A and B, symbol-digit, and other tests. Activation techniques have not yet been applied to map sites affected by HE, but recent data using the paced serial auditory addition test and an auditory continuous performance task have proven to be sensitive indicators in minimally impaired patients. The full potential of PET to evaluate neurotransmitter function is as yet unrealized.

Ammonia↗