The role of auditory cortex in retention of rhythmic patterns as studied in patients with temporal lobe removals including Heschl's gyrus.

This experiment examined the participation of the auditory cortex of the temporal lobe in the perception and retention of rhythmic patterns. Four patient groups were tested on a paradigm contrasting reproduction of auditory and visual rhythms: those with right or left anterior temporal lobe removals which included Heschl's gyrus (HG), the region of primary auditory cortex (RT-A and LT-A); and patients with right or left anterior temporal lobe removals which did not include HG (RT-a and LT-a). Estimation of lesion extent in HG using an MRI-based probabilistic map indicated that, in the majority of subjects, the lesion was confined to the anterior secondary auditory cortex located on the anterior-lateral extent of HG. On the rhythm reproduction task, RT-A patients were impaired in retention of auditory but not visual rhythms, particularly when accurate reproduction of stimulus durations was required. In contrast, LT-A patients as well as both RT-a and LT-a patients were relatively unimpaired on this task. None of the patient groups was impaired in the ability to make an adequate motor response. Further, they were unimpaired when using a dichotomous response mode, indicating that they were able to adequately differentiate the stimulus durations and, when given an alternative method of encoding, to retain them. Taken together, these results point to a specific role for the right anterior secondary auditory cortex in the retention of a precise analogue representation of auditory tonal patterns.

Psychosocial consequences of postoperative seizure relief.

To address the question of whether complete seizure relief has a positive effect on psychosocial functioning in patients with temporal lobe epilepsy, a follow-up study was conducted at the Montreal Neurological Institute. The approach was one of "before-after" study, with focus on the successfully operated patients, those in whom complete seizure relief was obtained. The Washington Psychosocial Seizure Inventory, specifically developed and validated for use with epilepsy patients, was used for psychosocial assessments. Of 30 surgically treated patients screened for the study, 15 gained complete relief from seizures. At 1-year postoperative follow-up, they showed reductions in their problems scores on all but one of eight psychosocial scales; the average reduction ranged from 24% in Vocational Adjustment to 60% in Adjustment to Seizures. In the areas of Emotional Adjustment and Interpersonal Adjustment reductions were 37 and 48%, respectively. Among the component items, improvement was greatest in ability to concentrate and make decisions, confidence in interpersonal skills, ability to express personal opinions, and perception by others. No appreciable changes occurred in the 15 patients who did not gain complete relief of seizures; indeed, on six of the eight scales they showed a modest increase in their problem scores. This study provides evidence that complete relief from seizures leads to appreciable improvements in psychosocial well-being, manifest as early as 1-year postoperatively, in young adult patients.

Influx of a choline analog to dog brain measured by positron emission tomography.

The influx of the 11C-labeled choline analog pyrrolidinocholine into tissue was measured in the brain of three dogs by positron emission tomography (PET). During the first 90 s after the intravenous bolus injection of the tracer, transfer of tracer from plasma to tissue was unidirectional. The influx constant for pyrrolidinocholine into intracranial tissue, Kin, was 0.017 ml/g/min (0.008 SD), and the initial volume of distribution, V0, was 0.08 ml/g (0.03 SD). The influx constant was at least five times larger than the value expected if simple diffusion were to account for tissue uptake. The method presented in this paper can be used to investigate the availability of plasma choline and its analogs to the living human brain and other tissue in degenerative diseases affecting the cholinergic system, and to provide in vivo information on a choline transport system.

The effect of spontaneous reperfusion on metabolic function in early human cerebral infarcts.

Twelve patients were studied within 48 hours of stroke using positron emission tomography to determine cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO2), oxygen extraction fraction, cerebral blood volume, cerebral pH (CpH), and cerebral metabolic rate for glucose (CMRGlc), the last calculated using published normal rate constants (CMRGlc[N]) and those for severe ischemia. In these studies, a cortical region of severe ischemia (I) was outlined, its metabolic and perfusion properties evaluated, and its length measured. The contralateral uninvolved cortical rim (C) in these patients and the cortical rim in 5 older normal patients were used for comparison. The length of region I correlated with the neurological deficit measured independently by a clinical scoring method. The 12 patients fell into two groups: Group I (8 patients), whose CBF in I was 9.3 +/- 2.5 ml/100 gm/min (mean +/- SEM) and was in every patient lower than that in C (33.1 +/- 2.2), and Group 2 (4 patients), whose CBF in I was 42.1 +/- 8.5 ml/100 gm/min and was in every case higher than that in C (28.2 +/- 1.5). In Group I, region I showed a CMRGlc(N)/CMRO2 ratio of 0.22 +/- 0.06 and a CpH of 6.83 +/- 0.06. In Group 2, the same ratio in the region I was 0.58 +/- 0.09 and the CpH was 7.12 +/- 0.05. The CMRGlc (N)/CMRO2 ratio for the contralateral hemisphere was comparable in the two groups. Our data suggest that, within 48 hours of the clinical onset of stroke, the ischemic cortex is already reperfused in one third of patients. Those ischemic regions with persistent hypoperfusion appear acidotic, whereas in the reperfused regions, despite evidence of an increased CMRGlc/CMRO2 ratio, acidosis is not evident. The implications of these findings for therapies proposed in acute human cerebral ischemia are discussed.

Positron emission tomography.

One of the most exciting new techniques introduced in the last ten years is positron emission tomography (PET). PET provides quantitative, three-dimensional images for the study of specific biochemical and physiological processes in the human body. This approach is analogous to quantitative in vivo autoradiography but has the added advantage of permitting non-invasive in vivo studies. PET scanning requires a small cyclotron to produce short-lived positron emitting isotopes such as oxygen-15, carbon-11, nitrogen-13 and fluorine-18. Proper radiochemical facilities and advanced computer equipment are also needed. Most important, PET requires a multidisciplinary scientific team of physicists, radiochemists, mathematicians, biochemists and physicians. This review analyses the most recent trends in imaging technology, radiochemistry, methodology, and clinical applications of positron emission tomography.