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Biomedical subjects

Jeremy D Schmahmann

Publications and source records attributed to Jeremy D Schmahmann.

13 recordsLinked to original sources
PubMed2007

Myocardial blood flow and oxygen consumption in patients with Friedreich's ataxia prior to the onset of cardiomyopathy.

OBJECTIVES: We tested the hypothesis, in patients with Friedreich's ataxia and no overt structural heart disease, that impairment of cardiac oxidative metabolism may be compensated for either by increased rest myocardial blood flow or more efficient oxygen consumption in performance of external work. BACKGROUND: Friedreich's ataxia is characterized by a mutant frataxin gene, which causes mitochondrial iron overload and impaired energy production. Further, it is frequently associated with cardiomyopathy. Studies using magnetic resonance spectroscopy, however, suggest impaired cardiac energetics even in the absence of structural heart disease. METHODS: Positron emission tomography measured rest myocardial blood flow (N-13-ammonia method) and myocardial oxygen consumption (11-C-acetate, Kmono) in Friedreich's ataxia patients (n=8; 31+/-5 years, mean+/-SD, four women) and healthy controls (n=8; 30+/-7 years, five women) matched for stroke work index and age. Stroke work index and power were determined by electrocardiogram gated positron emission tomography N-13-ammonia using modified Simpson's rule to compute left ventricular volumes. RESULTS: Neither stroke work index nor rest myocardial blood flow differed significantly between the groups. Although myocardial oxygen consumption was lower in Friedreich's ataxia (P<0.001), Kmono/rest myocardial blood flow, an index of myocardial oxygen extraction, did not differ between the groups. Power/Kmono, an index of the efficiency of myocardial oxygen consumption, was greater in Friedreich's ataxia (P<0.04). Rest myocardial blood flow normalized to rate pressure product was lower in Friedreich's ataxia (P<0.05). CONCLUSIONS: Prior to the onset of cardiomyopathy, selected patients with Friedreich's ataxia may compensate for impaired cardiac energetics through more efficient oxygen consumption rather than increased rest myocardial blood flow. The data illustrate a more general mechanism pertaining to metabolic regulation of myocardial blood flow and myocardial oxygen consumption.

Adult↗
PubMed2006

Evidence for reduced cerebellar volumes in trichotillomania.

BACKGROUND: Limited knowledge exists regarding the neurobiology of trichotillomania (TTM). Cerebellum (CBM) volumes were explored, given its role in complex, coordinated motor sequences. METHODS: Morphometric magnetic resonance imaging (MRI) scans were obtained for 14 female subjects with DSM-IV diagnoses of TTM and 12 age-, education-, and gender-matched normal control (NC) participants. Parcellation was performed utilizing a recently developed methodology to measure subterritory volumes of the CBM. Regions were defined based on knowledge of the structural and functional subunits of the CBM. RESULTS: As predicted, significant group differences were reported for CBM raw cortical volumes (p = .008) that survived correction for total brain volume (TBV; p = .037) and head circumference (HC; p = .011). A priori and post hoc group raw volume comparisons for CBM subterritories and functional clusters revealed many significant differences. However, most differences failed to withstand correction for total CBM volumes (TCV). Smaller volumes were consistently reported for the TTM versus NC cohorts. Total Massachusetts General Hospital Hair Pulling Scale (MGHHPS) scores were significantly inversely correlated with left primary sensorimotor cluster volumes (p = .008), with smaller volumes associated with more severe TTM symptoms. CONCLUSIONS: These findings implicate the CBM in the neurobiology of TTM, with reduced subterritory volumes reported for the TTM versus NC groups.

Adolescent↗
PubMed2006

Diagnosis and management of pathological laughter and crying.

Patients with various neurologic disorders exhibit exaggerated or inappropriate episodes of laughter, crying, or both without an apparent motivating stimulus or in response to stimuli that would not have elicited such an emotional response before the onset of the underlying disease. During these episodes, patients have difficulty controlling their emotional expression according to the contextual information. In contrast, patients with mood disorders have a pervasive and sustained change in their emotional experience and thus exhibit spells of laughter or crying because of an underlying mania or depression. This article focuses on the clinical presentation, diagnosis, prevalence, and proposed pathophysiological mechanisms of and available treatment options for this clinical phenomenon.

Affective Symptoms↗
PubMed2005

MRI-based surface-assisted parcellation of human cerebellar cortex: an anatomically specified method with estimate of reliability.

We revisit here a surface assisted parcellation (SAP) system of the human cerebellar cortex originally described in Makris, N., Hodge, S.M., Haselgrove, C., Kennedy, D.N., Dale, A., Fischl, B., Rosen, B.R., Harris, G., Caviness, V.S., Jr., Schmahmann, J.D., 2003. Human cerebellum: surface-assisted cortical parcellation and volumetry with magnetic resonance imaging. J Cogn Neurosci 15, 584-599. This system preserves the topographic and morphologic uniqueness of the individual cerebellum and allows for volumetric analysis and representation of multimodal structural and functional data on the cerebellar cortex. This methodology integrates features of automated routines of the program FreeSurfer as well as semi-automated and manual procedures of the program Cardviews to create 64 cerebellar parcellation units based on fissure information and anatomical landmarks of the cerebellar surface. Using this technique, we undertook the parcellation of ten cerebella by two independent raters. The reliability of the resulting parcellation units (64 total) was high, with an average Intraclass Correlation Coefficient (ICC) of 0.724 in the vermis and 0.853 in the hemispheres. Clusters of parcellation units were then created, based on lobar and connectivity data and functional hypotheses. These 36 clusters, when treated as anatomical units, had an average ICC of 0.933. Whereas the individual units provide a high level of detail and anatomical specificity, the clusters add flexibility to the analysis by providing higher reliability.

Algorithms↗
PubMed2004

Motor projections to the basis pontis in rhesus monkey.

Motor corticopontine studies suggest that the pons is topographically organized, but details remain unresolved. We used physiological mapping in rhesus monkey to define subregions in precentral motor cortex (M1), injected isotope tracers into M1 and the supplementary motor area (SMA), and studied projections to the basis pontis. Labeled fibers descend in the internal capsule (SMA in anterior limb and genu; M1 in posterior limb) and traverse the midsection of the cerebral peduncle, where SMA fibers are medial, and face, arm, and leg fibers are progressively lateral. Each motor region has unique terminations in the ipsilateral basis pontis and nucleus reticularis tegmenti pontis. Projections are topographically organized, preferentially in the caudal half of the pons, situated in close proximity to traversing corticofugal fibers. In nuclei that receive multiple inputs, terminations appear to interdigitate. Projections from the SMA-face region are most medial and include the median pontine nucleus. M1-face projections are also medial but are lateral to those from SMA-face. Hand projections are in medially placed curved lamellae in mid- and caudal pons. Dorsal trunk projections are in medial and ventral locations. Ventral trunk/hip projections encircle the peduncle in the caudal pons. Foot projections are heaviest caudally in laterally placed, curved lamellae. These results have relevance for anatomical clinical correlations in the human basis pontis. Furthermore, the dichotomy of motor-predominant caudal pons projections to cerebellar anterior lobe, contrasted with associative-predominant rostral pons projections to cerebellar posterior lobe, is consistent with new hypotheses regarding the cerebellar contribution to motor activity and cognitive processing.

Animals↗
PubMed2004

The human basis pontis: motor syndromes and topographic organization.

Clinical-anatomic correlations were performed in 25 patients with focal infarcts in the basilar pons to determine whether pontine lacunar syndromes conform to discrete clinical entities, and whether there is topographic organization of the motor system within the human basis pontis. Twelve clinical signs were scored on a 6-point scale, neuroimaging lesions were mapped and defined with statistical certainty, and structure-function correlation was performed to develop a topographic map of motor function. Clinical findings ranged from major devastation following extensive lesions (pure motor hemiplegia) to incomplete basilar pontine syndrome and restricted deficits after small focal lesions (ataxic hemiparesis, dysarthria-clumsy hand syndrome, dysarthria-dysmetria and dysarthria-facial paresis). The syndromes are not absolutely discrete, and are distinguished from each other by the relative degree of involvement of each clinical feature. Structure-function correlations indicate that strength is conveyed by the corticofugal fibres destined for the spinal cord, whereas dysmetria results from lesions involving the neurons of the basilar pons that link the ipsilateral cerebral cortex with the contralateral cerebellar hemisphere. Facial movement and articulation are localized to rostral and medial basilar pons; hand coordination is medial and ventral in rostral and mid-pons; and arm function is represented ventral and lateral to the hand. Leg coordination is in the caudal half of the pons, with lateral predominance. Swallowing is dependent upon the integrity of a number of regions in the rostral pons. Gait is in medial and lateral locations throughout the rostral- caudal extent of the pons. Dysmetria ipsilateral to the lesion constitutes a disconnection syndrome, as it occurs when the hemipontine lesion is extensive and interrupts pontocerebellar fibres traversing from the opposite, intact side of the pons. The heterogeneity of manifestations reflects the well-organized topography of motor function in the human basis pontis, in agreement with the anatomic organization of the motor corticopontine projections in the monkey. Higher order impairments including motor neglect, paraphasic errors and pathological laughter result from rostral and medial pontine lesions, and may result from disruption of the pontine component of associative corticopontocerebellar circuits.

Adult↗
PubMed2004

Ataxia after pontine stroke: insights from pontocerebellar fibers in monkey.

Basis pontis lacunes cause contralateral but rarely ipsilateral ataxia. We explored this phenomenon with isotope tract tracing in the rhesus monkey. Labeled pontocerebellar fibers cross midline and disperse widely in the opposite hemipons before coalescing in the brachium pontis. This anatomical arrangement suggests that small pontine strokes spare sufficient decussating pontocerebellar fibers to prevent ipsilateral dysmetria, and that ipsilateral dysmetria after large pontine stroke represents a disconnection syndrome.

Animals↗
PubMed2004

Disorders of the cerebellum: ataxia, dysmetria of thought, and the cerebellar cognitive affective syndrome.

Many diseases involve the cerebellum and produce ataxia, which is characterized by incoordination of balance, gait, extremity and eye movements, and dysarthria. Cerebellar lesions do not always manifest with ataxic motor syndromes, however. The cerebellar cognitive affective syndrome (CCAS) includes impairments in executive, visual-spatial, and linguistic abilities, with affective disturbance ranging from emotional blunting and depression, to disinhibition and psychotic features. The cognitive and psychiatric components of the CCAS, together with the ataxic motor disability of cerebellar disorders, are conceptualized within the dysmetria of thought hypothesis. This concept holds that a universal cerebellar transform facilitates automatic modulation of behavior around a homeostatic baseline, and the behavior being modulated is determined by the specificity of anatomic subcircuits, or loops, within the cerebrocerebellar system. Damage to the cerebellar component of the distributed neural circuit subserving sensorimotor, cognitive, and emotional processing disrupts the universal cerebellar transform, leading to the universal cerebellar impairment affecting the lesioned domain. The universal cerebellar impairment manifests as ataxia when the sensorimotor cerebellum is involved and as the CCAS when pathology is in the lateral hemisphere of the posterior cerebellum (involved in cognitive processing) or in the vermis (limbic cerebellum). Cognitive and emotional disorders may accompany cerebellar diseases or be their principal clinical presentation, and this has significance for the diagnosis and management of patients with cerebellar dysfunction.

Affective Symptoms↗
PubMed2003

Vascular syndromes of the thalamus.

BACKGROUND: This article reviews the anatomy, connections, and functions of the thalamic nuclei, their vascular supply, and the clinical syndromes that result from thalamic infarction. SUMMARY OF REVIEW: Thalamic nuclei are composed of 5 major functional classes: reticular and intralaminar nuclei that subserve arousal and nociception; sensory nuclei in all major domains; effector nuclei concerned with motor function and aspects of language; associative nuclei that participate in high-level cognitive functions; and limbic nuclei concerned with mood and motivation. Vascular lesions destroy these nuclei in different combinations and produce sensorimotor and behavioral syndromes depending on which nuclei are involved. Tuberothalamic territory strokes produce impairments of arousal and orientation, learning and memory, personality, and executive function; superimposition of temporally unrelated information; and emotional facial paresis. Paramedian infarcts cause decreased arousal, particularly if the lesion is bilateral, and impaired learning and memory. Autobiographical memory impairment and executive failure result from lesions in either of these vascular territories. Language deficits result from left paramedian lesions and from left tuberothalamic lesions that include the ventrolateral nucleus. Right thalamic lesions in both these vascular territories produce visual-spatial deficits, including hemispatial neglect. Inferolateral territory strokes produce contralateral hemisensory loss, hemiparesis and hemiataxia, and pain syndromes that are more common after right thalamic lesions. Posterior choroidal lesions result in visual field deficits, variable sensory loss, weakness, dystonia, tremors, and occasionally amnesia and language impairment. CONCLUSIONS: These vascular syndromes reflect the reciprocal cerebral cortical-thalamic connections that have been interrupted and provide insights into the functional properties of the thalamus.

Animals↗
PubMed2003

Human cerebellum: surface-assisted cortical parcellation and volumetry with magnetic resonance imaging.

We describe a system of surface-assisted parcellation (SAP) of the human cerebellar cortex derived from neural systems functional and behavioral anatomy. This system is based on MRI and preserves the unique morphologic and topographic features of the individual cerebellum. All major fissures of the cerebellum were identified and traced in the flattened representation of the cerebellar cortex using the program "FreeSurfer." Parcellation of the cerebellar cortex followed using the fissure information in conjunction with landmarks using the program "Cardviews" to create 64 gyral-based cerebellar parcellation units. Computer-assisted algorithms enable the execution of the cerebellar parcellation procedure as well as volumetric measurements and topographic localization. The SAP technique makes it possible to represent multimodal structural and functional imaging data on the flattened surface of the cerebellar cortex as illustrated in one functional MRI experiment.

Adult↗