William F. Eddy

Brain activation modulated by sentence comprehension

The comprehension of visually presented sentences produces brain activation that increases with the linguistic complexity of the sentence. The volume of neural tissue activated (number of voxels) during sentence comprehension was measured with echo-planar functional magnetic resonance imaging. The modulation of the volume of activation by sentence complexity was observed in a network of four areas: the classical left-hemisphere language areas (the left laterosuperior temporal cortex, or Wernickes area, and the left inferior frontal gyrus, or Brocas area) and their homologous right-hemisphere areas, although the right areas had much smaller volumes of activation than did the left areas. These findings generally indicate that the amount of neural activity that a given cognitive process engenders is dependent on the computational demand that the task imposes.

A Predictive Approach to Model Selection

Abstract This article offers a synthesis of Bayesian and sample-reuse approaches to the problem of high structure model selection geared to prediction. Similar methods are used for low structure models. Nested and nonnested paradigms are discussed and examples given.

Maturation of widely distributed brain function subserves cognitive development.

Cognitive and brain maturational changes continue throughout late childhood and adolescence. During this time, increasing cognitive control over behavior enhances the voluntary suppression of reflexive/impulsive response tendencies. Recently, with the advent of functional MRI, it has become possible to characterize changes in brain activity during cognitive development. In order to investigate the cognitive and brain maturation subserving the ability to voluntarily suppress context-inappropriate behavior, we tested 8-30 year olds in an oculomotor response-suppression task. Behavioral results indicated that adult-like ability to inhibit prepotent responses matured gradually through childhood and adolescence. Functional MRI results indicated that brain activation in frontal, parietal, striatal, and thalamic regions increased progressively from childhood to adulthood. Prefrontal cortex was more active in adolescents than in children or adults; adults demonstrated greater activation in the lateral cerebellum than younger subjects. These results suggest that efficient top-down modulation of reflexive acts may not be fully developed until adulthood and provide evidence that maturation of function across widely distributed brain regions lays the groundwork for enhanced voluntary control of behavior during cognitive development.

Graded Functional Activation in the Visuospatial System with the Amount of Task Demand

Two studies examined how the amount and type of computational demand are related to fMRI-measured activation in three bilateral cortical regions involved in the Shepard-Metzler (1971) mental-rotation paradigm. The amount of demand for the computation of visuospatial coordinates was manipulated by presenting mental rotation problems with increasing angular disparity (0, 40, 80, or 120). Activation in both the left and right intraparietal sulcal regions increased linearly with angular disparity in two separate studies. Activation also occurred in the fusiform gyrus and inferior temporal regions, regions that are primarily associated with the processes of object and object-part identification. By contrast, the demand for object recognition and rotation processes was relatively low, and the demand for executing saccades was high in a control condition that required making a systematic visual scan of two grids. The grid-scanning condition resulted in relatively less activation in the parietal and inferior temporal regions but considerable activation in frontal areas that are associated with planning and executing saccades, including the precentral gyrus and sulcus into the posterior middle frontal region. These data suggest that the amount of activation in the various cortical regions that support visuospatial processing is related to the amount, as well as to the type, of computational demand.

Neocortical system abnormalities in autism An fMRI study of spatial working memory

Objective To test the hypothesis that deficits in spatial working memory in autism are due to abnormalities in prefrontal circuitry. Methods Functional MRI (fMRI) at 3 T was performed in 11 rigorously diagnosed non–mentally retarded autistic and six healthy volunteers while they performed an oculomotor spatial working memory task and a visually guided saccade task. Results Autistic subjects demonstrated significantly less task-related activation in dorsolateral prefrontal cortex (Brodmann area [BA] 9/46) and posterior cingulate cortex (BA 23) in comparison with healthy subjects during a spatial working memory task. In contrast, activation of autistic individuals was not reduced in other regions comprising the neural circuitry for spatial working memory including the cortical eye fields, anterior cingulate cortex, insula, basal ganglia, thalamus, and lateral cerebellum. Autistic subjects also did not demonstrate reduced activation in any brain regions while performing visually guided saccades. ConclusionImpairments in executive cognitive processes in autism may be subserved by abnormalities in neocortical circuitry as evidenced by decreased activation in prefrontal and posterior cingulate circuitry during a spatial working memory task.

A New Convex Hull Algorithm for Planar Sets

A new algorithm, CONVEX, that determines which points of a planar set are vertices of the convex hull of the set is presented. It is shown that CONVEX operates in a fashion similar to the sorting algorithm QUICKERSORT. Evidence is given which indicates that in some situations CONVEX is preferable to earlier algorithms. A Fortran implementation, intended to minimize execution time, is presented and an alternative, which minimizes storage requirements, is discussed.

FUNCTIONAL BRAIN ABNORMALITIES ARE RELATED TO CLINICAL RECOVERY AND TIME TO RETURN-TO-PLAY IN ATHLETES

OBJECTIVE The relationship between athlete reports of symptoms, neurophysiological activation, and neuropsychological functioning is investigated in a sample of high school athletes. METHODS All athletes were evaluated using functional magnetic resonance imaging (fMRI), a computer-based battery of neurocognitive tests, and a subjective symptom scale. Athletes were evaluated within approximately 1 week of injury and again after clinical recovery using all assessment modalities. RESULTS This study found that abnormal fMRI results during the first week of recovery predicted clinical recovery. As a group, athletes who demonstrated hyperactivation on fMRI scans at the time of their first fMRI scan demonstrated a more prolonged clinical recovery than athletes who did not demonstrate hyperactivation at the time of their first fMRI scan. CONCLUSION These results demonstrate the relationship between neurophysiological, neuropsychological, and subjective symptom data in a relatively large sample composed primarily of concussed high school athletes. fMRI represents an important evolving technology for the understanding of brain recovery after concussion and may help shape return-to-play guidelines in the future.

Time Course of fMRI-Activation in Language and Spatial Networks during Sentence Comprehension

Functional neuroimaging previously has been considered to provide inadequate temporal resolution to study changes of brain states as a function of cognitive computations; however, we have obtained evidence of differential amounts of brain activity related to high-level cognition (sentence processing) within 1.5 s of stimulus onset. The study used an event-related paradigm with high-speed echoplanar functional magnetic resonance imaging (fMRI) to trace the time course of the brain activation in the temporal and parietal regions as participants comprehended single sentences describing a spatial configuration. Within the first set of images, on average 1 s from when the participant begins to read a sentence, there was significant activation in a key cortical area involved in language comprehension (the left posterior temporal gyrus) and visuospatial processing (the left and right parietal regions). In all three areas, the amount of activation during sentence comprehension was higher for negative sentences than for their affirmative counterparts, which are linguistically less complex. The effect of negation indicates that the activation in these areas is modulated by the difficulty of the linguistic processing. These results suggest a relatively rapid coactivation in both linguistic and spatial cortical regions to support the integration of information from multiple processing streams.

Functional Imaging Analysis Software — Computational Olio

Magnetic resonance imaging (MRI) is a modern technique for producing pictures of the internals of the human body. An MR scanner subjects its contents to carefully modulated electro-magnetic fields and records the resulting radio signal. The radio signal is the Fourier transform of the density of (for example) hydrogen atoms. Computing the inverse Fourier transform of the digitized signal reveals an image of the (hydrogen density of the) contents of the scanner. Functional MRI (fMRI) is a very recent development in which MRI is used to produce images of the human brain which show regions of activation reflecting the functioning of the brain.

THE CONVEX HULL OF A SPHERICALLY SYMMETRIC SAMPLE

Using the isomorphism between convex subsets of Euclidean space and continuous functions on the unit sphere we describe the probability measure of the convex hull of a random sample. When the sample is spherically symmetric the asymptotic behavior of this measure is determined. There are three distinct limit measures, each corresponding to one of the classical extreme-value