Biomedical subjects

Sally Durgerian

Publications and source records attributed to Sally Durgerian.

3 recordsLinked to original sources

PubMed2006

Functional magnetic resonance imaging response to increased verbal working memory demands among patients with multiple sclerosis.

Multiple sclerosis (MS) patients frequently experience impaired verbal working memory (VWM). Functional magnetic resonance imaging (fMRI) may help identify neural mechanisms underlying these deficits. Neuroimaging studies of healthy adults have characterized responses associated with increased VWM demands during the n-Back task, suggesting that this experimental paradigm could help identify neural correlates of VWM deficits among MS patients. Fifteen MS patients and 15 matched control participants completed the n-Back during whole-brain fMRI. Mean signal during adjacent 0-Back blocks was subtracted, on a voxel-wise basis, from mean signal observed during n-Back blocks. Resulting difference scores for 1-, 2-, and 3-Back were compared across groups and difficulty levels. Signal intensity was positively related to difficulty level in anterior regions, including premotor, supplementary motor, and dorsolateral prefrontal cortices. MS patients exhibited significantly greater intensity in these areas compared to controls during the 1-Back, while portions of the left superior frontal gyrus, cingulate, and parahippocampal gyri were relatively less intense at more difficult levels. MS group responses were slower during the 1-Back and tended to be slower during the 3-Back; however, accuracy did not differ at any level. Lesion load was positively related to only 1-Back activity and unrelated to any performance measure. Results suggest that compensatory activity occurs among MS patients matched on performance accuracy. Furthermore, compensatory activity occurs predominantly in regions associated with VWM, and this may decline relative to controls as task demands increase. These findings may help to explain why MS patient performance decreases as a function of effort on neuropsychological tests.

Brain↗

PubMed2004

Neural systems supporting timing and chronometric counting: an FMRI study.

At least two strategies are available to humans for estimating multisecond intervals. One depends on an interval timing system that is common to many species. The other is the language-based strategy of chronometric counting. These two strategies are easily distinguished by the psychophysical properties of their behavioral correlates: counting supports substantially more precise estimates than are possible using the more general interval timing system. The present study investigates the neural systems that underlie the execution of these different strategies. Eighteen adults reproduced a 16-s interval either by internally timing or covertly counting the duration. Comparison of counting and timing to a resting baseline suggested that these strategies engage some nonoverlapping neural systems. Counting, but not timing, strongly activated Broca's area, primary motor cortex in the mouth region, and right cerebellum, all of which are associated with internal speech. Counting also activated parts of the medial premotor circuit, including the putamen, supplementary motor area (SMA) proper, and cingulate motor area (CMA), that have been associated with reproducing isochronous and syncopated rhythms of elements lasting hundreds of milliseconds. During timing, only a portion of this circuit, the SMA proper and CMA, was engaged. Both timing and counting interfered with semantic processing during the resting state, evidenced by task-related decreases in the left inferior and middle frontal gyri, right superior frontal gyrus, left angular gyrus, and bilateral posterior cingulate cortex. This study suggests that counting activates a corticostriatal network associated with millisecond, rhythmic timing. In contrast, timing long durations without the benefit of linguistic strategies for subdividing counts reduces activity in this circuitry.

Adult↗

PubMed2004

Motor sequence complexity and performing hand produce differential patterns of hemispheric lateralization.

Studies in brain damaged patients conclude that the left hemisphere is dominant for controlling heterogeneous sequences performed by either hand, presumably due to the cognitive resources involved in planning complex sequential movements. To determine if this lateralized effect is due to asymmetries in primary sensorimotor or association cortex, whole-brain functional magnetic resonance imaging was used to measure differences in volume of activation while healthy right-handed subjects performed repetitive (simple) or heterogeneous (complex) finger sequences using the right or left hand. Advanced planning, as evidenced by reaction time to the first key press, was greater for the complex than simple sequences and for the left than right hand. In addition to the expected greater contralateral activation in the sensorimotor cortex (SMC), greater left hemisphere activation was observed for left, relative to right, hand movements in the ipsilateral left superior parietal area and for complex, relative to simple, sequences in the left premotor and parietal cortex, left thalamus, and bilateral cerebellum. No such volumetric asymmetries were observed in the SMC. Whereas the overall MR signal intensity was greater in the left than right SMC, the extent of this asymmetry did not vary with hand or complexity level. In contrast, signal intensity in the parietal and premotor cortex was greater in the left than right hemisphere and for the complex than simple sequences. Signal intensity in the caudal anterior cerebellum was greater bilaterally for the complex than simple sequences. These findings suggest that activity in the SMC is associated with execution requirements shared by the simple and complex sequences independent of their differential cognitive requirements. In contrast, consistent with data in brain damaged patients, the left dorsal premotor and parietal areas are engaged when advanced planning is required to perform complex motor sequences that require selection of different effectors and abstract organization of the sequence, regardless of the performing hand.

Adult↗