Alessandra M. Passarotti

Diffusion Tensor Imaging Study of White Matter Fiber Tracts in Pediatric Bipolar Disorder and Attention-Deficit/Hyperactivity Disorder

BACKGROUND To investigate microstructure of white matter fiber tracts in pediatric bipolar disorder (PBD) and attention-deficit/hyperactivity disorder (ADHD). METHODS A diffusion tensor imaging (DTI) study was conducted at 3 Tesla on age- and IQ-matched children and adolescents with PBD (n = 13), ADHD (n = 13), and healthy control subjects (HC) (n = 15). Three DTI parameters, fractional anisotropy (FA), apparent diffusion coefficient (ADC), and regional fiber coherence index (r-FCI), were examined in eight fiber tracts: anterior corona radiata (ACR), anterior limb of the internal capsule (ALIC), superior region of the internal capsule (SRI), posterior limb of the internal capsule (PLIC), superior longitudinal fasciculus (SLF), inferior longitudinal fasciculus (ILF), cingulum (CG), and splenium (SP). RESULTS Significantly lower FA was observed in ACR in both PBD and ADHD relative to HC. In addition, FA and r-FCI values were significantly lower in ADHD relative to PBD and HC in both the ALIC and the SRI. Further, ADC was significantly greater in ADHD relative to both the PBD and HC in ACR, ALIC, PLIC, SRI, CG, ILF, and SLF. CONCLUSIONS Decreased FA in ACR implies an impaired fiber density or reduced myelination in both PBD and ADHD in this prefrontal tract. These abnormalities, together with the reduced fiber coherence, extended to corticobulbar tracts in ADHD. Increased ADC across multiple white matter tracts in ADHD indicates extensive cellular abnormalities with less diffusion restriction in ADHD relative to PBD.

Neural correlates of response inhibition in pediatric bipolar disorder and attention deficit hyperactivity disorder.

Impulsivity, inattention and poor behavioral inhibition are common deficits in pediatric bipolar disorder (PBD) and attention deficit hyperactivity disorder (ADHD). This study aimed to identify similarities and differences in the neural substrate of response inhibition deficits that are associated with these disorders. A functional magnetic resonance imaging (fMRI) study was conducted on 15 unmedicated PBD patients (Type I, manic/mixed), 11 unmedicated ADHD patients, and 15 healthy controls (HC) (mean age = 13.5 years; S.D. = 3.5). A response inhibition task examined the ability to inhibit a motor response to a target when a stop cue appeared shortly after. The PBD and ADHD groups did not differ on behavioral performance, although both groups were less accurate than the HC group. fMRI findings showed that for trials requiring response inhibition, the ADHD group, relative to the PBD and HC groups, demonstrated reduced activation in both ventrolateral (VLPFC) and dorsolateral (DLPFC) prefrontal cortex, and increased bilateral caudate activation compared with HC. The PBD group, relative to HC, showed decreased activation in the left VLPFC, at the junction of the inferior and middle frontal gyri, and in the right anterior cingulate cortex (ACC). Prefrontal dysfunction was observed in both the ADHD and PBD groups relative to HC, although it was more extensive and accompanied by subcortical overactivity in ADHD.

Differential engagement of cognitive and affective neural systems in pediatric bipolar disorder and attention deficit hyperactivity disorder

This fMRI study investigates the neural bases of cognitive control of emotion processing in pediatric bipolar disorder (PBD) and attention deficit hyperactivity disorder (ADHD). Seventeen un-medicated PBD patients, 15 un-medicated ADHD patients, and 14 healthy controls (HC) (mean age = 13.78 +/- 2.47) performed an emotional valence Stroop Task, requiring them to match the color of an emotionally valenced word to the color of either of two adjacent circles. Both patient groups responded significantly slower than HC, but there were no group differences in accuracy. A voxel-wise analysis of variance on brain activation revealed a significant interaction of group by word valence [F(2,41) = 4.44; p = .02]. Similar group differences were found for negative and positive words. For negative versus neutral words, both patient groups exhibited greater activation in dorsolateral prefrontal cortex (DLPFC) and parietal cortex relative to HC. The PBD group exhibited greater activation in ventrolateral prefrontal cortex (VLPFC) and anterior cingulate cortex (ACC) relative to HC. The ADHD group exhibited decreased VLPFC activation relative to HC and the PBD group. During cognitive control of emotion processing, PBD patients deployed the VLPFC to a greater extent than HC. The ADHD patients showed decreased VLPFC engagement relative to both HC and PBD patients.

Face and place processing in Williams syndrome: evidence for a dorsal-ventral dissociation

Individuals with Williams syndrome (WMS) show an interesting dissociation of ability within the visuospatial domain, particularly between face perception and other visuospatial tasks. In this population, using tasks matched for stimuli, required response, and difficulty (for controls) is critical when comparing performance across these areas. We compared WMS individuals with a sample of typically developing 8- and 9-year-old children, and with a sample of adults, closer to the WMS participants in chronological age, in order to investigate performance across two precisely matched perceptual tasks, one assessing face processing and the other assessing proficiency in processing stimuli location. The pattern of performance seen in WMS, but not in controls, implicates a specific deficit of dorsal stream functioning in this syndrome.

A generalized role of interhemispheric interaction under attentionally demanding conditions: evidence from the auditory and tactile modality

The present study investigated whether dividing critical information across the hemispheres in the auditory and tactile modalities aids performance more for computationally complex rather than computationally simpler task-a pattern previously observed in the visual modality [Cortex 26 (1990) 77; Neuropsychology 12 (1998) 380; Neuropsychologia 30 (1992) 923]. We conducted two experiments, one in the auditory and one in the tactile modality, that were analogous to those previously performed in the visual modality. In agreement with previous findings, for both modalities we observed that the performance advantage exhibited for within-hemisphere processing in the computationally simpler condition (that required fewer steps to reach a decision) was diminished in the computationally more complex condition. In the auditory experiment we also manipulated computational complexity by varying the amount of time available for processing information. The within-hemisphere advantage in performance was also significantly reduced when complexity was increased through temporal manipulations. These findings suggest that the brain may use interhemispheric interaction as a general strategy to increase computational resources, independent of sensory modality and the manner in which computational demands are increased.

Interhemispheric interaction during childhood: II. Children with early-treated phenylketonuria

This study examined whether children with early-treated phenylketonuria (ETPKU) exhibited a disruption in communication between the hemispheres as a function of computational complexity (Banich & Belger, 1990; Belger & Banich, 1992, 1998) when compared to neurologically uncompromised children who were matched in age and IQ. This investigation was motivated by findings that phenylketonuria affects myelination of neurons, including those that make up the corpus callosum, the main neural conduit for interhemispheric interaction. Children performed 2 tasks: a less complex physical-identity task and a more complex name-identity task. For both tasks, we compared performance on across-hemisphere trials, which require interhemispheric interaction, and on within-hemisphere trials, in which no hemispheric interaction is required. On the more complex name-identity task, children with ETPKU exhibited less of a benefit from across-hemisphere processing than did neurologically intact children. These results suggest that the interhemispheric interaction required to complete computationally complex tasks is compromised in children with ETPKU. Such an insufficiency may explain some of the attentional deficits observed in this group of children.

Interhemispheric Interaction During Childhood: I. Neurologically Intact Children

This study examined the development of interaction between the hemispheres as a function of computational complexity (Banich & Belger, 1990; Belger & Banich, 1992) in 24 children aged 6.5 to 14 years. Participants performed 2 tasks: a less complex physical-identity task and a more complex name-identity task. Children, like adults, exhibit an across-hemisphere advantage on the computationally more complex name-identity task, and neither a within- nor an across-hemisphere advantage for the computationally less complex physical-identity task. Correlations indicated that the younger the child, (a) the greater the size of the within-hemisphere advantage on the less complex task, (b) the greater the size of the across-hemisphere advantage on the more complex task, and (c) the poorer the ability to ignore attentionally distracting information in a selective attention paradigm. These results suggest that interhemispheric interaction in children, like that in adults, serves to deal with the heightened processing demands imposed by increased computational complexity.