Showing papers by "Andrew P. Holmes published in 1995"

A functional neuroanatomy of hallucinations in schizophrenia

Abstract: HALLUCINATIONS, perceptions in the absence of external stimuli, are prominent among the core symptoms of schizophrenia. The neural correlates of these brief, involuntary experiences are not well understood, and have not been imaged selectively. We have used new positron emission tomography (PET) methods1,2 to study the brain state associated with the occurrence of hallucinations in six schizophrenic patients. Here we present a group study of five patients with classic auditory verbal hallucinations despite medication, demonstrating activations in subcortical nuclei (thalamic, stri-atal), limbic structures (especially hippocampus), and paralimbic regions (parahippocampal and cingulate gyri, as well as orbito-frontal cortex). We also present a case study of a unique, drug-naive patient with visual as well as auditory verbal hallucinations, demonstrating activations in visual and auditory/linguistic association cortices as part of a distributed cortical–subcortical network. Activity in deep brain structures, identified with group analysis, may generate or modulate hallucinations, and the particular neo-cortical regions entrained in individual patients may affect their specific perceptual content. The interaction of these distributed neural systems provides a biological basis for the bizarre reports of schizophrenic patients.

Relation between cerebral activity and force in the motor areas of the human brain.

Abstract: 1. Positron emission tomography (PET) studies were performed in six normal right-handed male volunteers (age 30 +/- 3) to investigate the relationship between cerebral activation as measured by relative regional cerebral blood flow (rCBF) and force peak exerted during right index finger flexion. The purpose was to determine in which central motor structures activity is directly correlated with force for repeatedly executed movements. 2. Twelve PET rCBF measurements were performed in each volunteer with the use of H2(15)O as a perfusion tracer. Volunteers pressed a Morse-key repetitively with their right index finger for 2 min while lying in a supine position in the PET camera. The device was fitted with strain gauges to measure the force peaks exerted upon it. Scans were collected twice each at five different levels of exerted force peak and in a resting state. Individual and group results were co-registered with anatomic magnetic resonance images (MRI). 3. Group analysis revealed four major regions with a high correlation between rCBF and different degrees of repetitively exerted force peaks. One was located in the arm area of the left lateral surface [primary somatosensory and motor cortex (SI, MI)]. The second area was situated on the left mesial surface of the brain, posterior to the anterior commissure (AC) and encompassing the first gyrus dorsal to the cingulate sulcus. This area is thought to be homologous to the posterior part of the supplementary motor area (SMA) in the monkey. The third area was the dorsal bank of the posterior cingulate sulcus. The fourth area showing a significant correlation between rCBF and force peaks was in the cerebellar vermis. 4. Individual PET data were co-registered with each individual's MRI in order to identify precisely the locations of structures demonstrating a positive correlation between rCBF and force peak. Activated areas on the mesial surface consisted of the same two distinct regions seen in the group data. In three subjects the focus on the lateral surface of the cortex appeared to extend into the caudal premotor area; in two it extended into the rostral part of the superior parietal area. In no subject did blood flow in the anterior cingulate areas and anterior SMA show a correlation with the force exerted. Cerebellar correlations were present in the vermis in all subjects.(ABSTRACT TRUNCATED AT 400 WORDS)

Estimating smoothness in statistical parametric maps: variability of p values.

Abstract: OBJECTIVE The smoothness parameter that characterises the spatial dependence of pixel values in functional brain images is usually estimated empirically from the data. Since this parameter is essential for the assessment of significant changes in brain activity, it is important to know (a) the variance of its estimator and (b) how this variability affects the results of the ensuing statistical analysis. MATERIALS AND METHODS In this article, we derive an approximate expression for the variance of the smoothness estimator and investigate the effects of this variability on assessing the significance of cerebral activation in statistical parametric maps using a verbal fluency PET activation experiment. RESULTS Our results suggest that, for p values around 0.05, the variability in the p value (due to smoothness estimation) is approximately 20%. CONCLUSION The effect of the assessment of the spatial dependency of the data is far from being negligible, and this suggests a more comprehensive methodology for functional imaging than the one used so far. This work provides a simple tool for taking into account this effect.