The relationship between global and local changes in PET scans

In order to localize cerebral cognitive or sensorimotor function, activation paradigms are being used in conjunction with PET measures of cerebral activity (e.g., rCBF). The changes in local cerebral activity have two components: a global, region independent change and a local or regional change. As the first step in localizing the regional effects of an activation, global variance must be removed by a normalization procedure. A simple normalization procedure is division of regional values by the whole brain mean. This requires the dependence of local activity on global activity to be one of simple proportionality. This is shown not to be the case. Furthermore, a systematic deviation from a proportional relationship across brain regions is demonstrated. Consequently, any normalization must be approached on a pixel-by-pixel basis by measuring the change in local activity and change in global activity. The changes associated with an activation can be partitioned into global and local effects according to two models: one assumes that the increase in local activity depends on global values and the other assumes independence. It is shown that the increase in activity due to a cognitive activation is independent of global activity. This independence of the (activation) condition effect and the confounding linear effect of global activity on observed local activity meet the requirements for an analysis of covariance, with the "nuisance" variable as global activity and the activation condition as the categorical independent variable. These conclusions are based on analysis of data from 24 scans: six conditions over four normal subjects using a verbal fluency paradigm.(ABSTRACT TRUNCATED AT 250 WORDS)

Positron emission tomography in psychiatric and neuropsychiatric disorders

PET is potentially the most powerful tool yet available for the direct, in vivo investigation of the biologic basis of psychiatric and neuropsychiatric disorders. The fulfillment of its potential rests on the development of methodologies and study design appropriate to psychiatric disorders. To date, findings in both schizophrenia and affective disorder, using protocols largely based on resting state data acquisition, suggest altered regional metabolism. These approaches need to be extended, particularly by the application of protocols that utilize PET to obtain longitudinal data under controlled experimental situations. In two conditions traditionally ascribed to psychologic causes, OCD and PD, there is intriguing evidence of specific biologic abnormalities, which, if confirmed, would lead to a fundamental revision of their nosologic status. In neuropsychiatric disorders PET findings, although preliminary in nature, offer an alternative paradigm to traditional clinicopathologic correlations by suggesting that clinical impairments relate to physiologic effects at sites distant from structural lesions.

Structural brain changes in patients with anorexia nervosa

Twenty-five patients with anorexia nervosa were compared with 17 normal healthy control subjects in terms of their cerebral computed tomographic (CT) scan appearances. The patients displayed significantly greater ventricular and sulcal enlargement when compared to control subjects. There were no relationships between the CT scan appearance and clinical indices of illness severity or weight loss in the patient group. In 14 patients who had repeat scans after attaining normal body weight, no significant change was observed in the ventricular appearance, but there was a significant lessening in the degree of sulcal widening.

The cerebral cortical appearance in depressed subjects

This paper describes a comparison of the cerebral cortical appearance of 101 patients with a history of clinical depression and 52 control subjects. An age-related increase in sulcal widening was evident in both groups. However, after controlling for age, the patients were found to differ from control subjects in two respects: they had a greater amount of sulcal widening, most noticeably in the frontal and temporal areas; and there was a positive correlation between increasing sulcal widening and increasing lateral ventricular size not found in the control subjects. Patients with a past history of treatment by electroconvulsive therapy showed more sulcal widening in the parietal and occipital areas than those not so treated.

The human growth hormone response to clonidine: relationship to clinical and neuroendocrine profile in depression

The authors found a significant negative correlation between human growth hormone (HGH) response to clonidine and urinary free cortisol level in 14 depressed patients. The HGH response did not distinguish endogenous depression from nonendogenous depression.

Cerebral ventricular size in depressed subjects

A computed tomographic study of 101 depressed patients and 52 normal control subjects is described. Increasing age and male sex were both associated with larger ventricular size in both patient and control groups. Controlling for these effects, the depressed patients had larger ventricles than the control subjects. In the patient group there was no association between ventricular size, course of illness or exposure to drug treatment or electroconvulsive therapy.

Life events, depression and hypothalamic-pituitary-adrenal axis function

The relationship between antecedent life events, clinical profile, and hypothalamic-pituitary-adrenal function was examined in 72 depressed patients. Antecedent life events were associated with first episodes of depression and with greater severity of illness, but their presence did not distinguish between patients diagnosed as endogenous or neurotic, and status on the dexamethasone suppression test was not associated with a greater or lesser likelihood of antecedent events. However, urinary free cortisol levels were higher in those patients with life events and difficulties.

Endocrine changes and clinical profiles in depression: II. The thyrotropin-releasing hormone test

Thirty-one (43%) of 68 patients with primary depression were found to have a blunted thyroid-stimulating hormone (TSH) response to thyrotropin-releasing hormone (TRH). Increased thyroid activity, as measured by the free thyroxine index (FTI), was present in 16 (24%) of the patients. Patients with blunted responses had a higher mean FTI level than those with normal responses. Patients with blunted responses were significantly more likely to exhibit the symptoms of depersonalization, derealization and agitation. There was no clear association between blunting and any particular diagnostic category of depression. Patients with blunted responses and high FTI values were more likely to report significant long-term environmental difficulties than patients with blunted responses and normal FTI values. It is suggested that there may be more than one mechanism responsible for blunting of the TSH response in depressed patients. In some patients blunting may be due to negative feedback from increased output of thyroid hormones, possibly released as part of a stress response. In other patients blunting may be due to a different mechanism, possibly involving pituitary gland dysfunction. These mechanisms would not necessarily be mutually exclusive in any one patient.

Endocrine changes and clinical profiles in depression: I. The dexamethasone suppression test

Hypothalamic-pituitary-adrenal axis function was investigated in 72 patients with primary depression. Forty-four per cent of the patients demonstrated abnormal suppression of their cortisol levels after a 1 mg overnight dexamethasone suppression test. Patients with abnormal suppression ('non-suppressors') were not clearly distinguished from 'suppressors' by the commonly used diagnostic classifications. They did not appear to be more severely depressed, but they were more likely than the 'suppressors' to be in-patients. Multivariate analysis of the data suggested that two clinical features were independently associated with non-suppression: the PSE syndromes of Slowness and General Anxiety. However, the association of these syndromes with non-suppression was relatively weak, indicating that the clinical significance of the dexamethasone suppression test is, as yet, unclear. The results raise doubts about the validity of using the dexamethasone suppression test as a diagnostic marker for a specific depressive syndrome.

Quantitative computed tomography in elderly depressed patients

An index of brain tissue density was obtained from the CT scans of 37 elderly depressed patients by measuring Hounsfield Units (HU) in 12 predefined brain areas. Comparisons were made with 23 patients suffering from senile dementia and 36 healthy controls. As a group the depressed patients resembled the dements more than the controls, although analysis of variance indicated differences between all three groups, controls showing the highest HU values and dements the lowest. In the depressed patients ventricular dilatation, which had already been shown to predict increased mortality, was also associated with lower HU levels. The significance of these and other findings is discussed.

ECT and cerebral atrophy. A computed tomographic study

The case-notes of 41 elderly depressives who underwent computed tomography were examined and the ECT history of each patient was assessed. No association was found between ECT and global cortical atrophy or ventricular size, but a significant relationship was demonstrated between frontal lobe atrophy and ECT.