Three macaque monkeys and 13 healthy human volunteers underwent diffusion tensor MRI with a 3 Tesla scanner for diffusion tract tracing (DTT) reconstruction of callosal bundles from different areas. In six macaque monkeys and three human subjects, the length of fiber tracts was obtained from histological data and combined with information on the distribution of axon diameter, so as to estimate callosal conduction delays from different areas. The results showed that in monkeys, the spectrum of tract lengths obtained with DTT closely matches that estimated from histological reconstruction of axons labeled with an anterogradely transported tracer. For each sector of the callosum, we obtained very similar conduction delays regardless of whether conduction distance was obtained from tractography or from histological analysis of labeled axons. This direct validation of DTT measurements by histological methods in monkeys was a prerequisite for the computation of the callosal conduction distances and delays in humans, which we had previously obtained by extrapolating the length of callosal axons from that of the monkey, proportionally to the brain volumes in the two species. For this analysis, we used the distribution of axon diameters from four different sectors of the corpus callosum. As in monkeys, in humans the shortest callosal conduction delays were those of motor, somatosensory, and premotor areas; the longer ones were those of temporal, parietal, and visual areas. These results provide the first histological validation of anatomical data about connection length in the primate brain based on DTT imaging.

Positron emission tomography was used to study the effects of unilateral vascular thalamic lesions on cortical oxygen and glucose utilization in 10 patients. There was significant ipsilateral cortex hypometabolism in 9 of the 10 patients, affecting the whole cortical mantle diffusely. The only patient spared was free of neuropsychological deficit at the time of positron emission tomography. In 4 patients, the magnitude of ipsilateral cortical hypometabolism was significantly less at a follow-up PET study, when neuropsychological function had improved When taken together, the 14 studies showed a significant tendency for the hypometabolism to improve with taken together, the 14 studies showed a significant tendency for the hypometabolism to improve with time after clinical onset. These data suggest that the ipsilateral cortical hypometabolism results from damage to the thalamo-cortical connections and reflect either loss of nonspecific activating afferences or a degenerative deafferentation-deefferentation process, or both. Its links with the concept of diaschisis are suggested by its tendency to recover. A causal relationship between cortical hypometabolism and neuropsychological deficit, however, although strongly suggested, cannot be firmly established from the present data.

In order to evaluate whether cortical motor reorganization occurs in the earliest phase of multiple sclerosis, we studied patients after a first clinical attack of hemiparesis. From a consecutive series of 70 patients enrolled in a study of patients with clinically isolated syndrome and serial MRI findings indicative of multiple sclerosis, we retrospectively selected 10 patients with hemiparesis as the onset symptom and no further clinical episode [mean age 32 ± 9 years, disease duration 24 ± 14 months, median Expanded Disability Status Score (EDSS) 1.25]. Ten age‐matched, healthy subjects served as controls. Each subject was submitted to two functional MRI trials (one per hand) using a 1.5 T magnet during a sequential finger‐to‐thumb opposition task. Image analysis was performed using SPM99 software. Movements of both the ‘affected’ and the ‘unaffected’ hand activated significantly larger areas in patients than in controls in both the contralateral and ipsilateral cortical motor areas. Patients activated a greater number of foci than controls during both the right‐hand and the left‐hand movement. Most of these foci were located in cortical areas which were less or not at all activated in controls, such as the lateral premotor cortex [Brodmann area (BA) 6], the insula and the inferior parietal lobule (BA 40). Between‐group analysis of patients versus controls showed significant (P < 0.001) foci in these areas, principally located in the ipsilateral hemisphere during right‐hand movement and in both the cerebral hemispheres during left‐hand movement. Time since clinical onset showed a significant positive correlation with the extent of activation in the ipsilateral motor areas (P = 0.006) during the right‐hand movement and with the extent of activation in both the ipsilateral (P = 0.02) and contralateral (P = 0.006) motor areas during the left‐hand movement. The T₁ lesion load along the motor pathway showed a significant positive correlation (P = 0.007) with the extent of activation in the contralateral motor areas during right‐hand movement. Our study shows functional adaptive changes that involve both the symptomatic and asymptomatic hemisphere during a simple motor task in patients who had suffered a single clinical attack of hemiparesis. The extent of these changes increased with the time elapsed since disease onset and the severity of brain damage.

During the first year of life, exchanges and communication between a mother and her infant are exclusively preverbal and are based on the mother's ability to understand her infant's needs and feelings (i.e., empathy) and on imitation of the infant's facial expressions; this promotes a social dialog that influences the development of the infant self. Sixteen mothers underwent functional magnetic resonance imaging while observing and imitating faces of their own child and those of someone else's child. We found that the mirror neuron system, the insula and amygdala were more active during emotional expressions, that this circuit is engaged to a greater extent when interacting with one's own child, and that it is correlated with maternal reflective function (a measure of empathy). We also found, by comparing single emotions with each other, that joy expressions evoked a response mainly in right limbic and paralimbic areas; by contrast, ambiguous expressions elicited a response in left high order cognitive and motor areas, which might reflect cognitive effort.

The main finding of this study is that functional connectivity changes in the thalamocortical network occur in patients with multiple sclerosis (MS) and correlate with cognitive performance, suggesting that characterization of patterns and dynamics of such a critical brain network may shed light on the development and progression of cognitive impairment in MS. PurposeTo investigate, by using resting-state (RS) functional magnetic resonance (MR) imaging, thalamocortical functional connectivity (FC) and its correlations with cognitive impairment in multiple sclerosis (MS).Materials and MethodsAll subjects provided written informed consent; the study protocol was approved by the university institutional review board for this HIPAA-compliant study. Forty-eight patients with relapsing-remitting MS and 24 control subjects underwent multimodal MR imaging, including diffusion-tensor imaging, three-dimensional (3D) T1-weighted imaging, and functional MR imaging at rest and a neuropsychological examination with the Paced Auditory Serial Addition Test (PASAT). Functional MR imaging data were analyzed with tools from FMRIB Software Library, by using the seed-based method to identify the thalamic RS network (RSN).ResultsWhen compared with control subjects, patients showed gray matter and white matter atrophy, as well as diffusion-tensor imaging abnormalities (P < .01). Pati...