R. J. Seitz

Human anterior intraparietal area subserves prehension: a combined lesion and functional MRI activation study.

It has been shown in nonhuman primates that the posterior parietal cortex is involved in coordination of arm and eye movements in space, whereas the anterior intraparietal area in the anterior lateral bank of the intraparietal sulcus plays a crucial role in fine finger movements, such as grasping. In this study we show by optoelectronic movement recordings that patients with cortical lesions involving the anterior lateral bank of the intraparietal sulcus have selective deficits in the coordination of finger movements required for object grasping, whereas reaching is much less disturbed. Patients with parietal lesions sparing the cortex lining the anterior intraparietal sulcus showed intact grasping behavior. Complementary evidence was obtained from functional MRI in normal control subjects showing a specific activation of the anterior lateral bank of the intraparietal sulcus during grasping. In conclusion, this combined lesion and activation study suggests that the anterior lateral bank of the intraparietal sulcus, possibly including the human homologue of the anterior intraparietal area, mediates the processing of sensorimotor integration of precisely tuned finger movements in humans.

Topography of interictal glucose hypometabolism in unilateral mesiotemporal epilepsy

We mapped the regional cerebral glucose metabolism (rCMRGlu) in 20 patients suffering from medically refractory focal epilepsy of either left or right mesiotemporal origin (mTLE) during resting wakefulness. After temporal lobectomy, histology demonstrated hippocampal sclerosis in 18 patients. Pixel-by-pixel comparisons with healthy control subjects showed significant (p <0.001) depressions of the mean rCMRGlu ipsilateral to the epileptic focus in the mesiotemporal region, including the hippocampus and the parahippocampal gyrus and middle temporal gyrus. Additional remote rCMRGlu depressions occurred bilaterally in the fronto-orbital cortex and ipsilaterally in the posterior insula and the thalamus. Patients with left-sided mTLE had additional rCMRGlu depressions in the left inferior frontal gyrus (Brocas region) and superior temporal gyrus at the parietotemporal junction, whereas corresponding rCMRGlu depressions were not present in patients with right mTLE. Neuropsychological testing showed impaired verbal fluency, verbal intelligence, and verbal memory in the left mTLE patients. Correlations of the specific mean rCMRGlu depressions and the neuropsychological deficits suggest that impaired language functions in patients with left mTLE could result from functional changes beyond the temporal lobe.

Recruitment of contralesional motor cortex in stroke patients with recovery of hand function.

In neuroimaging studies of stroke patients, coactivation may account for increased recruitment of bilateral motor areas when moving the affected limb. Here we studied eight patients after stroke with fMRI and simultaneous EMG. Bilateral recruitment of premotor and primary motor cortices was evident in five patients with strictly unilateral performance per EMG. Because patients had excellent motor recovery, this increased recruitment suggests an adaptive response to the infarct.

Conscious and subconscious sensorimotor synchronization--prefrontal cortex and the influence of awareness.

One of the most compelling challenges for modern neuroscience is the influence of awareness on behavior. We studied prefrontal correlates of conscious and subconscious motor adjustments to changing auditory rhythms using regional cerebral blood flow measurements. At a subconscious level, movement adjustments were performed employing bilateral ventral mediofrontal cortex. Awareness of change without explicit knowledge of the nature of change led to additional ventral prefrontal and premotor but not dorsolateral prefrontal activations. Only fully conscious motor adaptations to a changing rhythmic pattern showed prominent involvement of anterior cingulate and dorsolateral prefrontal cortex. These results demonstrate that while ventral prefrontal areas may be engaged in motor adaptations performed subconsciously, only fully conscious motor control which includes motor planning will involve dorsolateral prefrontal cortex.

Distinct cortico-cerebellar activations in rhythmic auditory motor synchronization

We investigated the role of the cerebellum in differential aspects of temporal control of rhythmic auditory motor synchronization using positron emission tomography (PET). Subjects tapped with their right index finger to metronome tones at a mean frequency of .8 Hz during 5 conditions: (1) an isochronous rhythm condition, (2) random changes in interval durations, and while the duration of rhythmic intervals was continuously time-modulated following a cosine-wave function at (3) 3%, (4) 7%, and (5) 20% of base interval. Anterior lobe cerebellar neuronal populations showed similar motor-associated activity across all conditions regardless of rhythmic time structure in vermal and hemispheric parts ipsilateral to the movements. Neuronal populations in bilateral anterior posterior lobe, especially in the simple lobule, increased their activity stepwise with each increase in tempo modulation from a steady beat. Neuronal populations in other parts of the posterior lobe showed an increase of activity only during the 20% condition, which involved conscious monitoring of rhythmic pattern synchronization, especially on the left side contralateral to the movements. Differential cerebellar activation patterns correspond to those in contralateral primary (primary sensorimotor), ipsilateral secondary (inferior parietal close to the intraparietal sulcus) and bilateral tertiary (dorsolateral prefrontal cortex) sensorimotor areas of the cerebral cortex, suggesting that distinct functional cortico-cerebellar circuits subserve differential aspects of rhythmic synchronization in regard to rhythmic motor control, conscious and subconscious response to temporal structure, and conscious monitoring of rhythmic pattern tracking.

Quantitation of Regional Cerebral Blood Flow with 15O-Butanol and Positron Emission Tomography in Humans

We describe the implementation and validation of a combined dynamic–autoradiographic approach for measuring the regional cerebral blood flow (rCBF) with 15O-butanol. From arterial blood data sampled at a rate of 1 s and list mode data of the cerebral radioactivity accumulated over 100 s, the time shift between blood and tissue curves, the dispersion constant DC, the partition coefficient p, and the CBF were estimated by least squares fitting. Using the fit results, a pixel-by-pixel parametrization of rCBF was computed for a single 40-s (autoradiographic) 15O-butanol uptake image. The mean global CBF found in 27 healthy subjects was 49 ± 8 ml 100 g−1 min−1. Gray and white matter rCBF were 83 ± 20 and 16 ± 3 ml 100 g−1 min−1, respectively, with a corresponding partition coefficient p of 0.77 ± 0.18 and 0.77 ± 0.29 ml/g in both compartments. The quantitative images resulted in a significantly higher gray matter rCBF than the autoradiographic images.

Ictal motor signs and interictal regional cerebral hypometabolism

Early motor manifestations are the main components of focal seizures involving the frontal lobe. We examined the relationship between the initial ictal motor manifestations and interictal abnormalities of cerebral glucose consumption (rCMRGlc) as assessed by PET in 48 consecutive patients with focal seizures of neocortical origin. Group data analysis revealed that patients with predominantly unilateral clonic seizures had a significant contralateral perirolandic hypometabolism and to a lesser degree a contralateral frontomesial hypometabolism. Patients with predominantly focal tonic manifestations showed a hypometabolism within the frontomesial and perirolandic regions that was unilateral in all patients with lateralized tonic seizures. Patients with versive seizures had mainly contralateral metabolic depressions without a consistent regional pattern. Patients with hypermotor seizures had metabolic depressions involving frontomesial, anterior cingulate, perirolandic, and anterior insular/frontal operculum areas. In all patient groups, bilateral and symmetric hypometabolism of the thalamus and cerebellum was observed. We propose that this pattern of distinctly abnormal metabolic brain regions demonstrates not only possible epileptogenic zones but also symptomatogenic brain regions as shown by the associations between clinical manifestations and sets of abnormal brain regions, particularly if epileptogenic zones are in a clinically silent neocortical brain region. The detection and possible differentiation of symptomatogenic and epileptogenic zones might improve the effectiveness of presurgical noninvasive studies.

Alexithymia and impaired facial affect recognition in multiple sclerosis

Despite the high relevance of emotion processing for social functioning, the study of the impairment of facial affect in multiple sclerosis (MS) has received little attention. Previous research reported evidence for emotion processing deficits but the nature and extent are not fully explained. Thirty-five MS patients underwent dedicated neuropsychological assessment of emotion processing using two facial affect recognition tasks and self-report measures of alexithymia. For comparison, healthy participants served as controls. Relative to healthy controls, MS patients were impaired in facial affect recognition on four of the six Ekman basic emotions, except happiness and disgust. The MS patients were more alexithymic than the healthy controls. These data provide evidence for deficits in the recognition of emotional face expressions and emotional introspection.

Communication with emblematic gestures: Shared and distinct neural correlates of expression and reception

Emblematic (or symbolic) gestures allow individuals to convey a variety of thoughts and emotions ranging from approval to hostility. The use of such gestures involves the execution of a codified motor act by the addresser and its perception and decoding by the addressee. To examine underlying common and distinct neural correlates, we used fMRI tasks in which subjects viewed video clips of emblematic one‐hand gestures. They were asked to (1) take the perspective of the addresser and imagine executing the gestures (“expression” condition), and to (2) take the perspective of the addressee and imagine being confronted with the gestures (“reception” condition). Common areas of activation were found in inferior frontal, medial frontal, and posterior temporal cortices with left‐hemispheric predominance as well as in the cerebellum. The distinction between regions specifically involved in the expression or reception condition partly resembled the dorsal and ventral stream dichotomy of visual processing with junctions in inferior frontal and medial prefrontal cortices. Imagery of gesture expression involved the dorsal visual stream as well as higher‐order motor areas. In contrast, gesture reception encompassed regions related to semantic processing, and medial prefrontal areas known to be involved in the process of understanding the intentions of others. In conclusion, our results provide evidence for a dissociation in representations of emblematic gesture processing between addresser and addressee in addition to shared components in language‐related areas. Hum Brain Mapp, 2012.

Disturbed functional brain interactions underlying deficient tactile object discrimination in Parkinson's disease

Somatosensory discrimination of cuboid objects was studied in a group of healthy volunteers and patients with Parkinsons disease using regional cerebral blood flow (rCBF) measurements obtained with positron emission tomography (PET) and 15O labeled water [H215O]. A 6‐[18F]‐fluoro‐L‐dopa (FDOPA) PET scan demonstrated that the patients may be grouped into those with normal and those with abnormally low FDOPA uptake in the caudate nucleus. The categorical group comparisons revealed that task‐induced rCBF increases were deficient in bilateral motor and sensory cortical areas in the Parkinson patients. Moreover, deficient rCBF increases were evident in the mesial and right dorsolateral prefrontal cortex for patients in a more advanced disease state, who showed low FDOPA uptake in the caudate nucleus. A principal component analysis (PCA), performed on the rCBF data, identified three patterns (principal components, PCs) that differentiated patients from normals. The first PC represented a right‐hemisphere dominant, bilateral group of brain areas known to be involved in tactile exploration. A second PC reflected a cortical‐subcortical pattern of functional interactions, comprising cortical areas important for working memory processes. The third group‐differentiating PC revealed a pattern of functional interactions involving bilateral temporo‐parieto‐occipital association cortices, which was consistent with a hypothesized supramodal network necessary for object discrimination. In an additional subgroup analysis, greater expression of the third PC pattern predicted greater caudate FDOPA uptake in patients. Our neuroimaging data revealed a disturbance of distinct patterns of brain functional interactions related to the sensorimotor deficit in Parkinsons disease and to deficits of cognitive information processing deficits in the more advanced stage of Parkinsons disease. Hum. Brain Mapping 11:131–145, 2000.