Andrew Simmons

Bio: Andrew Simmons is an academic researcher from King's College London. The author has contributed to research in topics: Functional magnetic resonance imaging & Diffusion MRI. The author has an hindex of 102, co-authored 460 publications receiving 36608 citations. Previous affiliations of Andrew Simmons include Karolinska Institutet & University of London.

Optimal strategies for measuring diffusion in anisotropic systems by magnetic resonance imaging.

Abstract: The optimization of acquisition parameters for precise measurement of diffusion in anisotropic systems is described. First, an algorithm is presented that minimizes the bias inherent in making measurements with a fixed set of gradient vector directions by spreading out measurements in 3-dimensional gradient vector space. Next, it is shown how the set of b—matrices and echo time can be optimized for estimating the diffusion tensor and its scalar invariants. The standard deviation in the estimate of the tensor trace in a water phantom was reduced by more than 40% and the artefactual anisotropy was reduced by more than 60% when using the optimized scheme compared with a more conventional scheme for the same scan time, and marked improvements are demonstrated in the human brain with the optimized sequences. Use of these optimal schemes results in reduced scan times, increased precision, or improved resolution in diffusion tensor images. Magn Reson Med 42:515‐ 525, 1999. r 1999 Wiley-Liss, Inc.

Social intelligence in the normal and autistic brain: an fMRI study.

Abstract: There is increasing support for the existence of 'social intelligence' [Humphrey (1984) Consciousness Regained], independent of general intelligence. Brothers et al. 1990) J. Cog. Neurosci., 4, 107-118] proposed a network of neural regions that comprise the 'social brain': the orbito-frontal cortex (OFC), superior temporal gyrus (STG) and amygdala. We tested Brothers' theory by examining both normal subjects as well as patients with high-functioning autism or Asperger syndrome (AS), who are well known to have deficits in social intelligence, and perhaps deficits in amygdala function [Bauman & Kemper (1988) J. Neuropath. Exp. Neurol., 47, 369]. We used a test of judging from the expressions of another person's eyes what that other person might be thinking or feeling. Using functional magnetic resonance imaging (fMRI) we confirmed Brothers' prediction that the STG and amygdala show increased activation when using social intelligence. Some areas of the prefrontal cortex also showed activation. In contrast, patients with autism or AS activated the fronto-temporal regions but not the amygdala when making mentalistic inferences from the eyes. These results provide support for the social brain theory of normal function, and the amygdala theory of autism.

Hypofrontality in attention deficit hyperactivity disorder during higher-order motor control: a study with functional MRI.

Abstract: Objective: Functional magnetic resonance imaging (MRI) was used to investigate the hypothesis that attention deficit hyperactivity disorder (ADHD) is associated with a dysfunction of prefrontal brain regions during motor response inhibition and motor timing. Method: Generic brain activation of seven adolescent boys with ADHD was compared to that of nine comparison subjects equivalent in sex, age, and IQ while they were performing a stop task, requiring inhibition of a planned motor response, and a motor timing task, requiring timing of a motor response to a sensory cue. Results: The hyperactive adolescents showed lower power of response in the right mesial prefrontal cortex during both tasks and in the right inferior prefrontal cortex and left caudate during the stop task. Conclusions: ADHD is associated with subnormal activation of the prefrontal systems responsible for higher-order motor control. Functional MRI is a feasible technique for investigation of neural correlates of ADHD. (Am J Psychiatry 1999; 156:891‐896)

A lateralized brain network for visuospatial attention

Abstract: Right hemisphere dominance for visuospatial attention is characteristic of most humans, but its anatomical basis remains unknown We report the first evidence in humans for a larger parieto-frontal network in the right than left hemisphere, and a significant correlation between the degree of anatomical lateralization and asymmetry of performance on visuospatial tasks Our results suggest that hemispheric specialization is associated with an unbalanced speed of visuospatial processing

Human biochemical genetics

Abstract: So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Alzheimer's Disease: Genes, Proteins, and Therapy

Abstract: Rapid progress in deciphering the biological mechanism of Alzheimer's disease (AD) has arisen from the application of molecular and cell biology to this complex disorder of the limbic and association cortices. In turn, new insights into fundamental aspects of protein biology have resulted from research on the disease. This beneficial interplay between basic and applied cell biology is well illustrated by advances in understanding the genotype-to-phenotype relationships of familial Alzheimer's disease. All four genes definitively linked to inherited forms of the disease to date have been shown to increase the production and/or deposition of amyloid β-protein in the brain. In particular, evidence that the presenilin proteins, mutations in which cause the most aggressive form of inherited AD, lead to altered intramembranous cleavage of the β-amyloid precursor protein by the protease called γ-secretase has spurred progress toward novel therapeutics. The finding that presenilin itself may be the long-sought γ-...