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Jennifer M Gurd

Publications and source records attributed to Jennifer M Gurd.

8 recordsLinked to original sources
PubMed2006

Hand preference and performance in 20 pairs of monozygotic twins with discordant handedness.

The differences between right (RH) and left (LH) handers reported in the literature on fine motor tasks, has traditionally been interpreted relative to purported functioning of the cerebral hemispheres. However, conclusive evidence for performance differences which are intrinsic to handedness per se is difficult to obtain unless left and right handers are compared who are similar in their genetic and environmental background. The present study therefore, employed a monozygotic (MZ) twin design which minimizes differences in genetic variation between the two groups. Forty female monozygotic twins (20 pairs) were selected on the basis of discordance of writing hand. Their laterality preferences were assessed and they were tested for differences on hand performance tasks (dot filling, finger tapping, and peg moving). The results revealed that on the hand and foot preference inventories, the right-handers were more strongly lateralized than their left-handed sisters, and that the left-handers had greater variation in their laterality scores. There were substantial correlations between preference and performance scores. The analyses not only revealed the obvious strong main effects of writing hand on performance tasks, but interaction effects of handedness on the peg-moving task. The dot filling task differentiated the writing versus non-writing hand considerably better than either of the other two performance tasks. However, no evidence was found to indicate that twins who wrote with their left hands showed poorer performance than their right-handed twin sisters.

Female↗
PubMed2004

Analysis of neural mechanisms underlying verbal fluency in cytoarchitectonically defined stereotaxic space--the roles of Brodmann areas 44 and 45.

We investigated neural activations underlying a verbal fluency task and cytoarchitectonic probabilistic maps of Broca's speech region (Brodmann's areas 44 and 45). To do so, we reanalyzed data from a previous functional magnetic resonance imaging (fMRI) [Brain 125 (2002) 1024] and from a cytoarchitectonic study [J. Comp. Neurol. 412 (1999) 319] and developed a method to combine both data sets. In the fMRI experiment, verbal fluency was investigated in 11 healthy volunteers, who covertly produced words from predefined categories. A factorial design was used with factors verbal class (semantic vs. overlearned fluency) and switching between categories (no vs. yes). fMRI data analysis employed SPM99 (Statistical Parametric Mapping). Cytoarchitectonic maps of areas 44 and 45 were derived from histologic sections of 10 postmortem brains. Both the in vivo fMRI and postmortem MR data were warped to a common reference brain using a new elastic warping tool. Cytoarchitectonic probability maps with stereotaxic information about intersubject variability were calculated for both areas and superimposed on the functional data, which showed the involvement of left hemisphere areas with verbal fluency relative to the baseline. Semantic relative to overlearned fluency showed greater involvement of left area 45 than of 44. Thus, although both areas participate in verbal fluency, they do so differentially. Left area 45 is more involved in semantic aspects of language processing, while area 44 is probably involved in high-level aspects of programming speech production per se. The combination of functional data analysis with a new elastic warping tool and cytoarchitectonic maps opens new perspectives for analyzing the cortical networks involved in language.

Adult↗
PubMed2003

Within-task switching in the verbal domain.

Task-switching, a term that covers a wide range of different cognitive processes, is a topic of considerable current interest. We draw particular attention to verbal within-task switching in neurological patients and healthy volunteers. The paradigm employs two types of fluency tasks: (i) semantic category verbal fluency in which subjects covertly produce words from a predefined superordinate semantic category and (ii) automatic speech tasks in which subjects produce words from overlearned sequences. In the single-category conditions, words are produced from one category at a time; in the switching conditions, words are produced alternately from three categories. For example, the semantic categories could be fruits, cars, and furniture and the automatic categories could be days of the week, letters of the alphabet, and months of the year. In a previous fMRI study of healthy volunteers, the main group effect of switching (semantic category and automatic speech) relative to single-category fluency (semantic category and automatic speech) showed significant activations (p < 0.05 corrected) only in bilateral superior posterior parietal cortex, Brain 125, 1024-1038). There was no significant prefrontal activation as a main effect of switching. In this paper we present further results from that experiment which show a surprising lack of consistent frontal lobe switch activations in single-subject analyses. These findings are discussed in relation to other neuroimaging studies of task-switching and the role of convergent neuropsychological data from patients with neurodegenerative disease.

Brain↗
PubMed2003

In search of the hidden: an fMRI study with implications for the study of patients with autism and with acquired brain injury.

The Embedded Figures Task involves a search for a target hidden in a more complex visual pattern. The task has been used to study local perception and visual search in a range of normal and pathological populations. After acquired brain damage, impairment on embedded figures is strongly associated with aphasia; in the context of developmental disorder, people with autism or with Asperger's syndrome are reliably found to be better than normal controls on the task. The current study employed functional MRI with healthy volunteers to elucidate the brain regions that are specifically involved in the local search aspects of the Embedded Figures Task. We did so by analyzing the neural activations that are implicated in the task over and above those involved in an easier visual search task and in a straightforward shape recognition task. Significant activations (P < 0.05, corrected) specific in the above sense to the Embedded Figures Task were found in left inferior and left superior parietal cortex and in left ventral premotor cortex (inferior frontal gyrus). By contrast, comparing the overall effect of visual search within geometric figures to pure recognition of geometric shapes revealed more widespread activations in parietal, occipital, cerebellar, and frontal areas bilaterally. The implications of these findings for some developmental and acquired pathologies of perceptual functioning are outlined. We also relate our results to studies of local/global processing in other tasks.

Adult↗
PubMed2002

Posterior parietal cortex is implicated in continuous switching between verbal fluency tasks: an fMRI study with clinical implications.

We investigated whether posterior parietal cortex controls attentional switching when the tasks involve neither spatial nor visual cognition. Normal volunteers were scanned using functional MRI (fMRI). In all conditions, subjects were required to covertly produce words in verbal fluency tasks. They did so at a rate of one every 2 s (with eyes closed) in response to an auditory beep. In the non-switching (NS) trials, subjects responded with a series of items from a prespecified semantic category (SC) (e.g. fruits or cars) and from overlearned sequences (OSs) (days of the week, months of the year or letters of the alphabet). Instructions as to which category items should be drawn from on a given run of trials were presented over fMRI-compatible earphones prior to each run. In the switching (S) trials, subjects produced a series of word triads from three SCs: for example, fruits, cars and furniture (e.g. pear, Mercedes, table.); and from three OSs: days of the week, months of the year and letters of the alphabet (e.g. Monday, January, A.). This design is factorial, with the factors verbal class (SC or OSs) and switching conditions (S or NS). Increases in neural activity (P < 0.05, corrected for multiple comparisons) were observed only in superior posterior parietal cortex bilaterally as a main effect of the S conditions compared with the NS conditions. When SC fluency was compared with OS fluency, significant activations were found in anterior cingulate cortex bilaterally, the left inferior frontal gyrus, the middle frontal gyrus bilaterally, frontal operculum bilaterally and in the cerebellar vermis. These results support the hypothesis that superior posterior parietal cortex is a supramodal area implicated in task switching, even when no visual or spatial component is implicated in the tasks. Task switching, frequently used to examine 'frontal' executive functions, may also be clinically relevant to the assessment of patients with superior posterior parietal lesions.

Adult↗