Biomedical subjects

Peter T Fox

Publications and source records attributed to Peter T Fox.

At least 37 records · Page 2Linked to original sources

PubMed2005

Age-related morphology trends of cortical sulci.

The age-related trends of the width and the depth of major cortical sulci were studied in normal adults. Ninety healthy subjects (47 males, 43 females) age 20-82 years were evaluated. Measurements of average sulcal width and depth in 14 prominent sulcal structures per hemisphere were performed with high-resolution anatomical MRI. The average sulcal width increased at a rate of about 0.7 mm/decade, while the average sulcal depth decreased at a rate of about 0.4 mm/decade. Sulcal age-related trends were found to be highly influenced by gender in the superior temporal, collateral, and cingulate sulci (P < 0.05), with males showing more pronounced age-related change in sulcal width than females. Sulcal structures located in multimodal cortical areas showed more profound age-related changes than sulcal structures in unimodal cortical areas (P < 0.05).

Adult↗

PubMed2005

Testing the three-pool white matter model adapted for use with T2 relaxometry.

A three-pool model was used to improve white-matter T2 relaxometry in low signal-to-noise (SNR) data. To verify the model very high SNR T2 relaxometry experiments were performed on myelinated tissue samples and three-pool fractions were consistently found. Relaxation curves based on the in vitro results were simulated with multiple SNRs and fit using the three-pool model and three less constraining nonnegative least squares-based methods. All methods performed well with noiseless data. At lower SNR values the three-pool model was superior, primarily due to the fact that the other methods often could not unambiguously calculate pool fractions.

Algorithms↗

PubMed2005

The brain basis of piano performance.

Performances of memorized piano compositions unfold via dynamic integrations of motor, perceptual, cognitive, and emotive operations. The functional neuroanatomy of such elaborately skilled achievements was characterized in the present study by using (15)0-water positron emission tomography to image blindfolded pianists performing a concerto by J.S. Bach. The resulting brain activity was referenced to that for bimanual performance of memorized major scales. Scales and concerto performances both activated primary motor cortex, corresponding somatosensory areas, inferior parietal cortex, supplementary motor area, motor cingulate, bilateral superior and middle temporal cortex, right thalamus, anterior and posterior cerebellum. Regions specifically supporting the concerto performance included superior and middle temporal cortex, planum polare, thalamus, basal ganglia, posterior cerebellum, dorsolateral premotor cortex, right insula, right supplementary motor area, lingual gyrus, and posterior cingulate. Areas specifically implicated in generating and playing scales were posterior cingulate, middle temporal, right middle frontal, and right precuneus cortices, with lesser increases in right hemispheric superior temporal, temporoparietal, fusiform, precuneus, and prefrontal cortices, along with left inferior frontal gyrus. Finally, much greater deactivations were present for playing the concerto than scales. This seems to reflect a deeper attentional focus in which tonically active orienting and evaluative processes, among others, are suspended. This inference is supported by observed deactivations in posterior cingulate, parahippocampus, precuneus, prefrontal, middle temporal, and posterior cerebellar cortices. For each of the foregoing analyses, a distributed set of interacting localized functions is outlined for future test.

Adult↗

PubMed2005

Acute intravenous low- and high-dose cocaine reduces quantitative global and regional cerebral blood flow in recently abstinent subjects with cocaine use disorder.

Cocaine-induced hypoperfusion, a risk factor for ischemic stroke, has not been fully characterized during experimental drug-taking among individuals with cocaine use disorder. We sought to examine cocaine's dose-dependent, time-related effects on cerebral blood flow. In a double-blind, randomized human laboratory study with a counterbalanced order of drug administration, 31 male and female subjects with cocaine use disorder were divided into two groups receiving either (a) low-dose cocaine (0.325 mg/kg intravenously) or placebo (N=15) or (b) high-dose cocaine (0.650 mg/kg intravenously) or placebo (N=16). The different dose conditions were administered on test days separated by a rest period of >or=48 h. Cerebral blood flow was assessed quantitatively using H(2)O(15) positron emission tomography. Experimentally administered low- and high-dose cocaine conditions versus their corresponding placebo conditions were associated with global and regional hypoperfusion. The trend for high- versus low-dose cocaine to be associated with greater hypoperfusion achieved statistical significance only for the dopamine-rich sublobar and midbrain regions. Cocaine's hypoperfusion effects were maximal at 8 mins after infusion (i.e., at about the expected peak of intravenous cocaine levels) and had mostly dissipated by 32 mins after infusion. Although hypoperfusion occurred throughout the brain, the left hemispheric dopamine-rich sublobar region was the most severely affected. Cocaine-induced cerebral hypoperfusion is associated with the time course of its pharmacological effects, and dopamine-rich areas, particularly in the left hemisphere, may be most vulnerable. Increasingly larger doses of cocaine may be associated with greater risk for ischemic stroke.

Adolescent↗

PubMed2005

Non-invasive quantification of cerebral blood flow for rats by microPET imaging of 15O labelled water: the application of a cardiac time-activity curve for the tracer arterial input function.

OBJECTIVE: In-vivo quantitative cerebral blood flow (CBF) measurement using positron emission tomography (PET) has typically employed invasive arterial blood sampling procedure to determine the arterial input function (AIF). The present study was performed to provide a non-invasive quantitative CBF measurement technique for rats using a dedicated animal PET. METHODS: CBF was measured in 10 male rats (Fischer 344, 247-290 g) under alpha-chloralose anesthesia (30 mg x kg . h, intravenous infusion) by dynamic PET imaging employing the intravenous bolus injection of H2(15)O. Unlike other conventional PET methods, no arterial blood sampling was employed. Instead, a cardiac time-activity curve (TAC) obtained from the dynamic PET imaging was used to determine the AIF. For the validation of this technique, CBF was also measured by calculating the washout rate of the tracer (H2(15)O) following an intracarotid bolus injection. CBF measurements by two independent methods were done while modulating and maintaining the body temperature at two different levels (32+/-1 and 37+/-1 degrees C by the rectal temperature). Two methods were compared by the linear regression analysis. RESULTS: CBF (ml x 100 g x min) values (mean+/-SD) were 45.2+/-6.05 (intravenous) and 47.4+/-8.64 (intracarotid) at the hypothermic condition (32 degrees C), and 55.1+/-4.88 (intravenous) and 54.4+/-4.60 (intracarotid) at the normothermic condition (37 degrees C). There was a good agreement between the two methods (r=0.70). CONCLUSIONS: Our cardiac TAC analysis technique for small animals can be used for the non-invasive quantification of CBF using the PET-based in-vivo imaging technique.

Animals↗

PubMed2005

Prefrontal and executive attention network lesions and the development of attention-deficit/hyperactivity symptomatology.

OBJECTIVE: To investigate the association between focal stroke lesions of Posner's executive attention network and a specific region of interest in the frontal lobes (orbital frontal and mesial frontal) and either attention-deficit/hyperactivity disorder (ADHD) or traits of the disorder (ADHD symptomatology). METHOD: Twenty-nine children with focal stroke lesions were studied with standardized psychiatric assessments and anatomical brain magnetic resonance imaging. The pattern of lesion overlap in subjects with ADHD symptomatology was determined. RESULTS: Fifteen of 28 subjects with no prestroke ADHD were diagnosed with ADHD symptomatology at the time of assessment. The extent of lesions within the executive attention network was marginally related to ADHD symptomatology (p = .088; effect size = 0.66), whereas the extent of lesions in the specific frontal region of interest was significantly related to ADHD symptomatology (p = .040; effect size = 0.82). CONCLUSIONS: Lesions within Posner's executive attention network and its orbital frontal connections may be linked to important mechanisms in the expression of ADHD symptomatology after childhood stroke. These findings are consistent with functional and structural imaging findings in studies of idiopathic ADHD.

Attention Deficit Disorder with Hyperactivity↗

PubMed2005

BrainMap: the social evolution of a human brain mapping database.

Human brain mapping is an experimental discipline that establishes structure-function correspondences in the brain through the combined application of experimental psychology, human neuroscience, and noninvasive neuroimaging. A deep and diverse literature on the functional organization of the human brain is emerging, which has pushed neuroimaging squarely into the scientific mainstream. Because of this rapid growth, there is a great need to effectively collect and synthesize the body of literature in this field. The BrainMap database was created in response to this need as an electronic environment for modeling the human brain through quantitative meta-analysis of the brain mapping literature. BrainMap was originally conceived in 1987 and has received continuous funding from 1988 to 2004. During this time, BrainMap has consistently evolved to meet the challenges of an ever-changing field and continues to strive toward higher levels of applicability. In this article, we discuss BrainMap's structure and utility, and relate its progress and development as a neuroinformatics tool.

Brain Mapping↗

PubMed2005

Myelination in children with partial deletions of chromosome 18q.

BACKGROUND AND PURPOSE: We compared myelin levels in white matter (WM) in typically developing children with those of children with partial deletions of chromosome 18q (18q-). METHODS: Conventional spin-echo MR imaging at 1.9T was used to acquire T1-, T2-, and proton density-weighted images of the brain. From these images, a three-pool model was used to estimate the fraction of water in myelin, myelinated axon, and mixed water compartments (or pools) in six WM regions. A model curve was fit to the pool fractions to model the trend of myelin development by age in each region. Water-pool fractions in children with 18q- aged 5 months to 13 years were compared with those of age-matched, typically developing children. RESULTS: In children with 18q-, the model predicted later onset of myelination (P <.02), lower myelination rates (P <.001), and smaller equilibrium myelin pool fractions (P <.001). Significant differences were seen between the two groups for all three water pool fractions (P <.001). The mixed pool fraction was larger in children with 18q-. Although the myelin pool fraction was significantly smaller, the myelinated axon pool fraction was only slightly smaller, leading to a significantly smaller estimate of myelin per myelinated axon in children with 18q- (P <.001). CONCLUSION: Myelination modeling in 18q- children indicated delayed onset, a lower rate of myelination, and equilibrium myelin levels less than 50% those of age-matched, typically developing children.

Axons↗

PubMed2004

Column-based model of electric field excitation of cerebral cortex.

A model to explain the orientation selectivity of the neurophysiologic effects of electric-field transients applied to cerebral cortex is proposed and supported with neuroimaging evidence. Although it is well known that transcranial magnetic stimulation (TMS) excites cerebral cortex in an orientation-selective manner, a neurophysiologically compelling explanation of this phenomenon has been lacking. It is generally presumed that TMS-induced excitation is mediated by horizontal fibers in the cortical surfaces nearest to the stimulating coil, i.e., at the gyral crowns. No evidence exists, however, that horizontal fibers are orientation selective either anatomically or physiologically. We used positron emission tomography to demonstrate that TMS-induced cortical activation is selectively sulcal. This observation allows the well-established columnar organization of cerebral cortex to be invoked to explain the observed orientation selectivity. In addition, Rushton's cosine principle can used to model stimulation efficacy for an electrical field applied at any cortical site at any intensity and in any orientation.

Adult↗

PubMed2004

The song system of the human brain.

Although sophisticated insights have been gained into the neurobiology of singing in songbirds, little comparable knowledge exists for humans, the most complex singers in nature. Human song complexity is evidenced by the capacity to generate both richly structured melodies and coordinated multi-part harmonizations. The present study aimed to elucidate this multi-faceted vocal system by using 15O-water positron emission tomography to scan "listen and respond" performances of amateur musicians either singing repetitions of novel melodies, singing harmonizations with novel melodies, or vocalizing monotonically. Overall, major blood flow increases were seen in the primary and secondary auditory cortices, primary motor cortex, frontal operculum, supplementary motor area, insula, posterior cerebellum, and basal ganglia. Melody repetition and harmonization produced highly similar patterns of activation. However, whereas all three tasks activated secondary auditory cortex (posterior Brodmann Area 22), only melody repetition and harmonization activated the planum polare (BA 38). This result implies that BA 38 is responsible for an even higher level of musical processing than BA 22. Finally, all three of these "listen and respond" tasks activated the frontal operculum (Broca's area), a region involved in cognitive/motor sequence production and imitation, thereby implicating it in musical imitation and vocal learning.

Adult↗

PubMed2004

CBF changes during brain activation: fMRI vs. PET.

The changes in regional cerebral blood flow (rCBF) associated with the changes in neuronal activity are routinely measured both by positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) techniques. However, direct comparison has not been performed to determine similarities and differences of PET and fMRI techniques in determining the rCBF response to brain activation. In the present study, a quantitative comparison of the functional rCBF maps obtained by PET and fMRI are made by performing an activation study in a single group of subjects under precisely controlled conditions and using identical visual stimuli. Twelve healthy volunteers participated in the activation study using the visual checkerboard stimulation with flip frequency at 8 Hz. By selecting the conjunctive pixels which activated on both PET and fMRI maps, the change in rCBF measured by fMRI was 36.95 +/- 2.54%, whereas the value measured by PET was 38.79 +/- 2.63%. Our results have demonstrated that there is no statistically significant difference (P = 0.22) in the measurements of rCBF change between MRI and PET methods.

Algorithms↗

PubMed2004

Neural systems for word meaning modulated by semantic ambiguity.

One important issue in neuroimaging research on language is how the brain processes and represents lexical semantics. Past studies with various paradigms reveal that the left inferior prefrontal and mid-superior temporal regions play a crucial role in semantic processing. Those studies, however, typically utilize words having a precise and dominant meaning as stimuli and have not manipulated lexico-semantic ambiguity, a key feature of human language, as an experimental variable. Here, we used a word generation paradigm to examine whether neuroanatomical networks for meaning are modulated by lexical ambiguity. We found that, compared with semantically precise words, semantically ambiguous words were mediated by strong brain activations in the left dorsal-lateral frontal areas, the anterior cingulate, and the right inferior parietal lobe. Semantically precise words, instead, were associated with the left inferior prefrontal and mid-superior temporal sites. These findings indicate that semantic analysis of written words is a dynamic process involving coordination of widely distributed neural subsystems, which are weighted by semantic ambiguity.

Adult↗

PubMed2004

Is left inferior frontal gyrus a general mechanism for selection?

Converging lines of research in neuroimaging recognize selection as one of the critical functions of prefrontal cortex (e.g., see Annu. Rev. Neurosci. 24, 2001 167). We examined a central thesis of a selection hypothesis (Neuropsychologia 41, 2003 280) that the left inferior frontal gyrus (LIFG) serves as a general mechanism for selecting among competing representations (Annu. Rev. Neurosci. 18, 1995 193). Participants were presented with two sets of letters to remember and then cued to select one set from the two as the target set for subsequent recognition. LIFG showed significantly more activation when the cue elicited a strong need for selection, relative to when it did not, suggesting that the involvement of this area in selection is generalizable beyond semantic retrieval tasks as originally found. This result provides supporting evidence for the selection hypothesis.

Adult↗

PubMed2004

More workload on the central executive of working memory, less attention capture by novel visual distractors: evidence from an fMRI study.

The present study examined the interaction of the central executive in working memory with visual attention. Native Chinese participants were given two versions of a number subtraction task, one of low demand and one of high demand, and were asked to ignore a simultaneously presented peripheral distractor. The distractor could be Chinese or Korean characters, familiar or novel to participants, respectively. Compared with the low-demand subtraction task, brain regions commonly associated with central executive functions, including left middle prefrontal cortex, anterior cingulate cortex, and precentral gyrus/sulcus, were significantly activated in the high-demand task. Critically, there was a significant interaction between distractor type and task demand. Novel distractors captured attention and elicited automatic visual analysis, shown by primary visual cortex activation, only when the subtraction task was of low demand but not when it was of high demand. The results provide confirmatory evidence that the extent to which higher level cognitive resources, specifically, the central executive component of working memory, are absorbed by a cognitive task has an impact upon automatic processing that occurs in response to distracting items.

Adult↗

PubMed2004

Verbal learning and memory after childhood stroke.

Verbal learning and memory (VLM) following pediatric stroke was characterized in a cross-sectional neuropsychological and neuroimaging study of 26 subjects, aged 5 to 17, with a history of pediatric stroke and 26 age, SES, and gender matched orthopedic controls. Further comparisons were made between the VLM profiles of stroke subjects with right versus left hemisphere lesions and early (> 12 months) versus late (12 months) strokes. Overall, stroke subjects scored significantly lower than control subjects on several VLM indices (California Verbal Learning Test-Children; CVLT-C), as well as on measures of intellectual functioning (IQ) and auditory attention/working memory (Digit Span). Subgroup analyses of the stroke population found no significant differences in VLM, Digit Span, Verbal IQ or Performance IQ when left-hemisphere lesion subjects were compared to right-hemisphere lesion subjects. In contrast, early strokes were associated with significantly fewer words recalled after delay, reduced discriminability (fewer correct hits relative to false positive errors on recognition testing), and relatively worse auditory attention/working memory scores (Digit Span). These findings indicate that pediatric stroke subjects demonstrated more VLM impairment than control subjects, and early strokes were associated with greater recall and recognition deficits. In stark contrast with adult-onset stroke, both left- and right-hemisphere lesions during childhood resulted in similar VLM performance.

Adolescent↗

PubMed2004

Attention function after childhood stroke.

We investigated attentional outcome after childhood stroke and orthopedic diagnosis in medical controls. Twenty-nine children with focal stroke lesions and individually matched children with clubfoot or scoliosis were studied with standardized attention and neuroimaging assessments. Stroke lesions were quite varied in location and commonly involved regions implicated in Posner's model of attention networks. Children with stroke lesions performed significantly more poorly regarding attention function compared with controls. Performance on the Starry Night, a test demanding alerting and sensory-orienting but not executive attention function, was significantly associated with lesion size in the alerting and sensory-orienting networks but not the executive attention network. Furthermore, earlier age at lesion acquisition was significantly associated with poorer attention function even when lesion size was controlled. These findings support the theory of dissociable networks of attention and add to evidence from studies of children with diffuse and focal brain damage that early insults are associated with worse long-term outcomes in many domains of neuropsychological function. In addition, these results may provide clues towards the understanding of mechanisms underlying attention in children.

Adolescent↗

PubMed2004

Brain correlates of stuttering and syllable production: gender comparison and replication.

This article reports a gender replication study of the P. T. Fox et al. (2000) performance correlation analysis of neural systems that distinguish between normal and stuttered speech in adult males. Positron-emission tomographic (PET) images of cerebral blood flow (CBF) were correlated with speech behavior scores obtained during PET imaging for 10 dextral female stuttering speakers and 10 dextral, age- and sex-matched normally fluent controls. Gender comparisons were made between the total number of voxels per region significantly correlated with speech performance (as in P. T. Fox et al., 2000) plus total voxels per region that were significantly correlated with stutter rate and not with syllable rate. Stutter-rate regional correlates were generally right-sided in males, but bilateral in the females. For both sexes the positive regional correlates for stuttering were in right (R) anterior insula and the negative correlates were in R Brodmann area 21/22 and an area within left (L) inferior frontal gyrus. The female stuttering speakers displayed additional positive correlates in L anterior insula and in basal ganglia (L globus pallidus, R caudate), plus extensive right hemisphere negative correlates in the prefrontal area and the limbic and parietal lobes. The male stuttering speakers were distinguished by positive correlates in L medial occipital lobe and R medial cerebellum. Regions that positively correlated with syllable rate (essentially stutter-free speech) in stuttering speakers and controls were very similar for both sexes. The findings strengthen claims that chronic developmental stuttering is functionally related to abnormal speech-motor and auditory region interactions. The gender differences may be related to differences between the genders with respect to susceptibility (males predominate) and recovery from chronic stuttering (females show higher recovery rates during childhood).

Adult↗

PubMed2003

Neural systems of second language reading are shaped by native language.

Reading in a second language (L2) is a complex task that entails an interaction between L2 and the native language (L1). To study the underlying mechanisms, we used functional magnetic resonance imaging (fMRI) to visualize Chinese-English bilinguals' brain activity in phonological processing of logographic Chinese and alphabetic English, two written languages with a sharp contrast in phonology and orthography. In Experiment 1, we found that phonological processing of Chinese characters recruits a neural system involving left middle frontal and posterior parietal gyri, cortical regions that are known to contribute to spatial information representation, spatial working memory, and coordination of cognitive resources as a central executive system. We assume that the peak activation of this system is relevant to the unique feature of Chinese that a logographic character has a square configuration that maps onto a monosyllabic unit of speech. Equally important, when our bilingual subjects performed a phonological task on English words, this neural system was most active, whereas brain areas mediating English monolinguals' fine-grained phonemic analysis, as demonstrated by Experiment 2, were only weakly activated. This suggests that our bilingual subjects were applying their L1 system to L2 reading and that the lack of letter-to-sound conversion rules in Chinese led Chinese readers to being less capable of processing English by recourse to an analytic reading system on which English monolinguals rely. Our brain imaging findings lend strongest support to the idea that language experience tunes the cortex.

Adult↗