Biomedical subjects

Thomas A Hammeke

Publications and source records attributed to Thomas A Hammeke.

5 recordsLinked to original sources

PubMed2006

Task-modulation of functional synchrony between spontaneous low-frequency oscillations in the human brain detected by fMRI.

Recent developments in functional MRI (fMRI) technology with high spatial and temporal resolution have made it possible to noninvasively detect spontaneous low-frequency oscillations (SLOs) and quantify their functional synchrony in the human brain. In the present fMRI study the dynamic characteristics of the functional synchrony between SLOs were quantitatively determined by the phase shift index (PSI). With the use of an fMRI-guided voxel-selection method, the SLOs and their functional synchrony were found to be modulated by different memory tasks. The results demonstrate that SLOs in episodic memory-related circuitry have significantly higher synchrony during the performance of declarative memory-encoding activities compared to nondeclarative memory-encoding activities. It is suggested that the dynamic property of SLOs and the quantitative assessment of their functional synchrony could be utilized as a biomarker to noninvasively characterize localized pathophysiological functions in the human brain.

Adult↗

PubMed2005

A comparison of two FMRI protocols for eliciting hippocampal activation.

PURPOSE: Previous research suggests that the hippocampus is modulated both by stimulus novelty and by the extent to which relational processing (formation of associations) occurs during episodic encoding. The aim of this study was to compare hippocampal activation patterns measured by functional magnetic resonance imaging (fMRI) during encoding protocols emphasizing either novelty or relational processing. METHODS: fMRI was performed on 32 healthy volunteers while they encoded complex visual scenes or unrecognizable scrambled versions of the same scenes. In the Novelty contrast, encoding of novel scenes was compared with encoding of a repeated pair of scenes. In the Relational Processing contrast, semantic encoding of novel scenes was compared with structural encoding of scrambled scenes. RESULTS: Both protocols elicited bilateral hippocampal activation. Overall mean activation values were similar for the two protocols, but the Relational Processing protocol resulted in a larger volume of hippocampal activation. The pattern of activation along the longitudinal hippocampal axis differed for the two protocols. The Novelty contrast produced stronger activation in the posterior hippocampus, whereas the Relational Processing contrast produced stronger activation in the anterior hippocampus. CONCLUSIONS: Hippocampal activation is determined by both stimulus novelty and degree of relational processing during encoding. Given the importance of anterior hippocampal pathology in temporal lobe epilepsy, an approach emphasizing modulation of relational processing may be preferable for clinical fMRI of the medial temporal lobes.

Adolescent↗

PubMed2002

Functional neuroimaging in neurology and psychiatry.

How can functional neuroimaging be applied to clinical neurology and psychiatry? This article reviews selected contributions of functional neuroimaging to the clinical neurosciences. We review selected technical aspects of positron emission tomography, single photon emission tomography, and functional magnetic resonance imaging with a focus on the relative strengths and weaknesses of these techniques. Consumers of functional neuroimaging research are encouraged to consider the limitations of imaging techniques and theoretical pitfalls of cognitive task design when interpreting results of functional imaging studies. Then, we selectively review the contributions of functional neuroimaging to neurology and psychiatry, including the areas of epilepsy, stroke, chronic pain, schizophrenia, depression, and obsessive-compulsive disorder. Future directions of functional neuroimaging research are offered, with the emphasis that the best conclusions are informed by a convergence of research from functional neuroimaging, neurophysiological, and lesion studies.

Journal Article↗

PubMed2002

Neural basis of the Stroop interference task: response competition or selective attention?

Previous neuroimaging studies of the Stroop task have postulated that the anterior cingulate cortex (ACC) plays a critical role in resolution of the Stroop interference condition. However, activation of the ACC is not invariably seen and appears to depend on a variety of methodological factors, including the degree of response conflict and response expectancies. The present functional MRI study was designed to identify those brain areas critically involved in the interference condition. Healthy subjects underwent a blocked-trial design fMRI experiment while responding to 1 of 3 stimulus conditions: (1) incongruent color words, (2) congruent color words, and (3) color-neutral words. Subjects responded to the printed color of the word via a manual response. Compared to the congruent and neutral conditions, the incongruent condition produced significant activation within the left inferior precentral sulcus (IpreCS) located on the border between the inferior frontal gyrus, pars opercularis (BA 44) and the ventral premotor region (BA 6). Significant deactivations in the rostral component of the ACC and the posterior cingulate gyrus were also observed. Selective activation of the left IpreCS is compatible with findings from previous neuroimaging, lesion, electrophysiological, and behavioral studies and is presumably related to the mediation of competing articulatory demands during the interference condition.

Adolescent↗

PubMedDate not supplied

Normative data on 372 stimuli for descriptive naming.

Naming problems are common in patients with dominant temporal lobe epilepsy (TLE) and anterior temporal lobectomy (ATL). Descriptive naming may be an especially useful procedure for the presurgical workup of candidates for ATL, given its sensitivity for detecting subtle naming problems in TLE and its localization to anterior temporal regions that are commonly targeted for resection in ATL. This study provides normative data pertaining to difficulty level (accuracy and reaction time) on 372 descriptive naming items in four conceptual categories: common non-living, common living, unique non-living, and unique living things. These data will be useful to investigators who wish to develop protocols for clinical assessment or stimuli for functional imaging paradigms aimed at assessing the function of the anterior temporal lobes.

Adolescent↗