Aerobic exercise has been suggested to ameliorate aging-related decline in humans. Recently, evidence has indicated chronological aging is associated with decreases in measures of interhemispheric inhibition during unimanual movements, but that such decreases may be mitigated by long-term physical fitness. The present study investigated measures of ipsilateral (right) primary motor cortex activity during right-hand movements using functional magnetic resonance imaging and transcranial magnetic stimulation (TMS). Healthy, right-handed participant groups were comprised of 12 sedentary older adults, 12 physically active older adults, and 12 young adults. Active older adults and younger adults evidenced longer ipsilateral silent periods (iSP) and less positive BOLD of ipsilateral motor cortex (iM1) as compared to sedentary older adults. Across groups, duration of iSP from TMS was inversely correlated with BOLD activity in iM1 during unimanual movement. These findings suggest that increased physical activity may have a role in decreasing aging-related losses of interhemispheric inhibition.

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Despite over 140 years of research on Broca's area, the connections of this region to medial frontal cortex remain unclear. The current study investigates this structural connectivity using diffusion weighted MRI tractography in living humans. Our results show connections between Broca's area and Brodmann's areas (BA) 9, 8, and 6 (both supplementary motor area (SMA) in caudal BA 6, and Pre-SMA in rostral BA 6). Trajectories follow an anterior-to-posterior gradient, wherein the most anterior portions of Broca's area connect to BA 9 and 8 while posterior Broca's area connects to Pre-SMA and SMA. This anterior-posterior connectivity gradient is also present when connectivity-based parcellation of Broca's area is performed. Previous studies of language organization suggest involvement of anterior Broca's area in semantics and posterior Broca's area in syntax/phonology. Given corresponding patterns of functional and structural organization of Broca's area, it seems well warranted to investigate carefully how anterior vs. posterior medial frontal cortex differentially affect semantics, syntax and phonology.

In the recent decades structural connectivity between Broca's area and the basal ganglia has been postulated in the literature, though no direct evidence of this connectivity has yet been presented. The current study investigates this connectivity using a novel diffusion-weighted imaging (DWI) fiber tracking method in humans in vivo. Our findings suggest direct connections between sub-regions of Broca's area and the anterior one-third of the putamen, as well as the ventral anterior nucleus of the thalamus. Thus, we are the first to provide a detailed account of inferred circuitry involving basal ganglia, thalamus, and Broca's area, which would be a prerequisite to substantiate their support of language processing.

BackgroundFocal dystonia is a neurological disorder characterized by unwanted muscle spasms. Blepharospasm is a focal dystonia producing an involuntary closure of the eyelid. Its etiology is unknown.ObjectiveTo investigate if there are structural changes in the white and grey matter of blepharospasm patients, and if the changes are related to disease features.MethodsT1 and diffusion-weighted magnetic resonance imaging scans were collected from 14 female blepharospasm patients and 14 healthy matched controls. Grey matter volumes, fractional anisotropy (FA), and mean diffusivity maps were compared between the groups. Based on grey matter differences within the facial portion of the primary motor cortex, the corticobulbar tract was traced and compared between groups.ResultsChanges in grey matter in patients included the facial portion of the sensorimotor area and anterior cingulate gyrus. These changes did not correlate with disease duration. Corticobulbar tract volume and peak tract connectivity were decreased in patients compared with controls. There were no significant differences in FA or mean diffusivity between groups.ConclusionsGrey matter changes within the primary sensorimotor and the anterior cingulate cortices in blepharospasm patients may help explain involuntary eyelid closure and the abnormal sensations often reported in this condition.

The human brainstem is critical for the control of many life-sustaining functions, such as consciousness, respiration, sleep, and transfer of sensory and motor information between the brain and the spinal cord. Most of our knowledge about structure and organization of white and gray matter within the brainstem is derived from ex vivo dissection and histology studies. However, these methods cannot be applied to study structural architecture in live human participants. Tractography from diffusion-weighted magnetic resonance imaging (MRI) may provide valuable insights about white matter organization within the brainstem in vivo. However, this method presents technical challenges in vivo due to susceptibility artifacts, functionally dense anatomy, as well as pulsatile and respiratory motion. To investigate the limits of MR tractography, we present results from high angular resolution diffusion imaging of an intact excised human brainstem performed at 11.1 T using isotropic resolution of 0.333, 1, and 2 mm, with the latter reflecting resolution currently used clinically. At the highest resolution, the dense fiber architecture of the brainstem is evident, but the definition of structures degrades as resolution decreases. In particular, the inferred corticopontine/corticospinal tracts (CPT/CST), superior (SCP) and middle cerebellar peduncle (MCP), and medial lemniscus (ML) pathways are clearly discernable and follow known anatomical trajectories at the highest spatial resolution. At lower resolutions, the CST/CPT, SCP, and MCP pathways are artificially enlarged due to inclusion of collinear and crossing fibers not inherent to these three pathways. The inferred ML pathways appear smaller at lower resolutions, indicating insufficient spatial information to successfully resolve smaller fiber pathways. Our results suggest that white matter tractography maps derived from the excised brainstem can be used to guide the study of the brainstem architecture using diffusion MRI in vivo.

Introduction This study examined the reliability of high angular resolution diffusion tensor imaging (HARDI) data collected on a single individual across several sessions using the same scanner. Methods HARDI data was acquired for one healthy adult male at the same time of day on ten separate days across a one-month period. Environmental factors (e.g. temperature) were controlled across scanning sessions. Tract Based Spatial Statistics (TBSS) was used to assess session-to-session variability in measures of diffusion, fractional anisotropy (FA) and mean diffusivity (MD). To address reliability within specific structures of the medial temporal lobe (MTL; the focus of an ongoing investigation), probabilistic tractography segmented the Entorhinal cortex (ERc) based on connections with Hippocampus (HC), Perirhinal (PRc) and Parahippocampal (PHc) cortices. Streamline tractography generated edge weight (EW) metrics for the aforementioned ERc connections and, as comparison regions, connections between left and right rostral and caudal anterior cingulate cortex (ACC). Coefficients of variation (CoV) were derived for the surface area and volumes of these ERc connectivity-defined regions (CDR) and for EW across all ten scans, expecting that scan-to-scan reliability would yield low CoVs. Results TBSS revealed no significant variation in FA or MD across scanning sessions. Probabilistic tractography successfully reproduced histologically-verified adjacent medial temporal lobe circuits. Tractography-derived metrics displayed larger ranges of scanner-to-scanner variability. Connections involving HC displayed greater variability than metrics of connection between other investigated regions. Conclusions By confirming the test retest reliability of HARDI data acquisition, support for the validity of significant results derived from diffusion data can be obtained.

The defining symptoms of transcortical motor aphasia (TCMA) are nonfluent verbal output with relatively preserved repetition. Other symptoms, such as naming difficulties, agrammatic output, or even some paraphasias, may occur, but these are not cardinal symptoms defining TCMA and are not necessary for the diagnosis. The core anatomy involved in TCMA is a lesion of the medial frontal cortex, especially the left presupplementary motor area (pre-SMA) and adjacent Brodmann’s area 32; a lesion of the left posterior inferior frontal cortex, especially pars opercularis and ventral lateral premotor cortex; or a lesion of the pathways between these frontal structures. TCMA occasionally has been reported with a lesion of the left basal ganglia, the left thalamus, or the ascending dopaminergic pathways. From a cognitive standpoint, TCMA can be conceptualized as a disorder of intention, in other words, as a disorder of initiation and continuation of spoken language that is internally motivated. The medial frontal cortex provides the impetus to speak; this impetus to speak is conveyed to lateral frontal structures through frontal–subcortical pathways where it activates various language production mechanisms. The influence of the ascending dopaminergic pathways may occur either through their heavy connections with the pre-SMA region or through their influence on the basal ganglia. The influence of the basal ganglia and thalamus probably occurs through their connections with the medial frontal cortex. Assessments for TCMA should involve a thorough evaluation of conversational or narrative language output and repetition. New treatments are available that attempt to engage right-hemisphere intention mechanisms with left-hand movements and may be effective in TCMA. Although dopamine agonists have also shown some positive effects in increasing verbal output in TCMA, trials have been small, and some caution must be exercised in interpreting these findings.