Kyung K. Peck

Role of the Right and Left Hemispheres in Recovery of Function during Treatment of Intention in Aphasia

Two patients with residual nonfluent aphasia after ischemic stroke received an intention treatment that was designed to shift intention and language production mechanisms from the frontal lobe of the damaged left hemisphere to the right frontal lobe. Consistent with experimental hypotheses, the first patient showed improvement on the intention treatment but not on a similar attention treatment. In addition, in keeping with experimental hypotheses, the patient showed a shift of activity to right presupplementary motor area and the right lateral frontal lobe from pre-to post-intention treatment functional magnetic resonance imaging (fMRI) of language production. In contrast, the second patient showed improvement on both the intention and attention treatments. During pre-treatment fMRI, she already showed lateralization of intention and language production mechanisms to the right hemisphere that continued into post-intention treatment imaging. From pre-to post-treatment fMRI of language production, both patients demonstrated increased activity in the posterior perisylvian cortex, although this activity was lateralized to left-hemisphere language areas in the second but not the first patient. The fact that the first patients lesion encompassed almost all of the dominant basal ganglia and thalamus whereas the second patients lesion spared these structures suggests that the dominant basal ganglia could play a role in spontaneous reorganization of language production functions to the right hemisphere. Implications regarding the theoretical framework for the intention treatment are discussed.

Effect of brain tumor neovasculature defined by rCBV on BOLD fMRI activation volume in the primary motor cortex.

We utilized blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) and MR perfusion imaging methods to study the influence of brain tumor neovascularity on the BOLD fMRI activation volume in the primary motor cortex (PMC). The results from 57 brain tumor cases demonstrated that, for grade IV gliomas only, decreases in the BOLD fMRI activation volumes within the ipsilateral PMC, when compared with that observed in the contralateral PMC, correlated with increases in the relative regional cerebral blood volume (rCBV) in the PMC. In addition, relative increases in the activation volumes, corresponding to decreases in the rCBV, exhibited a linear dependence on the distance between the grade IV glioma and PMC. These findings lend support to the hypothesis that decreases in the fMRI activation volumes adjacent to a GBM may, in part, be due to the increased contribution of aberrant tumor neovascularity, with the resultant de-coupling of blood flow from neuronal activity. The nature of the relationship between the resulting activation volumes and adjacent tumor characteristics is complex, but is found to be dependent on the tumor grade and type, as well as the distance of the tumor to the PMC.

Functional Magnetic Resonance Imaging Before and After Aphasia Therapy Shifts in Hemodynamic Time to Peak During an Overt Language Task

Background and Purpose— Comparing the temporal characteristics of hemodynamic responses in activated cortical regions of aphasic patients before and after therapy would provide insight into the relationship between improved task performance and changes in blood oxygenation level–dependent (BOLD) functional MRI (fMRI) signal. This study investigated differences in the time to peak (TTP) of hemodynamic responses in activated regions of interest (ROIs), before and after therapy, and related them to changes in task performance. Methods— Three aphasic patients and 3 controls overtly generated a single exemplar in response to a category. For the patients, TTP of hemodynamic responses in selected ROIs was compared before and after language therapy. The timing differences between auditory cues and verbal responses were compared with TTP differences between auditory and motor cortices. Results— The selected ROIs were significantly activated in both aphasic patients and controls during overt word generation. In the aphasic patients, both the timing difference from auditory cues to verbal responses and the TTP difference between auditory and motor cortices decreased after rehabilitation, becoming similar to the values found in controls. Conclusions— Findings indicate that (1) rehabilitation increased the speed of word-finding processes; (2) TTP analysis was sensitive to this functional change and can be used to represent improvement in behavior; and (3) it is important to monitor the behavioral performance that might correlate with the temporal pattern of the hemodynamic response.

Comparison of hemodynamic response nonlinearity across primary cortical areas

Hemodynamic responses to auditory and visual stimuli and motor tasks were assessed for the nonlinearity of response in each of the respective primary cortices. Five stimulus or task durations were used (1, 2, 4, 8, and 16 s), and five male subjects (aged 19 +/- 1.9 years) were imaged. Two tests of linearity were conducted. The first test consisted of using BOLD responses to short stimuli to predict responses to longer stimuli. The second test consisted of fitting ideal impulse response functions to the observed responses for each event duration. Both methods show that the extent of the nonlinearity varies across cortices. Results for the second method indicate that the hemodynamic response is nonlinear for stimuli less than 10 s in the primary auditory cortex, nonlinear for tasks less than 7 s in the primary motor cortex, and nonlinear for stimuli less than 3 s in the primary visual cortex. In addition, neural adaptation functions were characterized that could model the observed nonlinearities.

Regional Changes in Word-Production Laterality After a Naming Treatment Designed to Produce a Rightward Shift in Frontal Activity

Five nonfluent aphasia patients participated in a picture-naming treatment that used an intention manipulation (opening a box and pressing a button on a device in the box with the left hand) to initiate naming trials and was designed to re-lateralize word production mechanisms from the left to the right frontal lobe. To test the underlying assumption regarding re-lateralization, patients participated in fMRI of category-member generation before and after treatment. Generally, the four patients who improved during treatment showed reduced frontal activity from pre- to post-treatment fMRI with increasing concentration of activity in the right posterior frontal lobe (motor/premotor cortex, pars opercularis), demonstrating a significant shift in lateraliity toward the right lateral frontal lobe, as predicted. Three of these four patients showed no left frontal activity by completion of treatment, indicating that right posterior lateral frontal activity supported category-member generation. Patients who improved in treatment showed no difference in lateralization of lateral frontal activity from normal controls pre-treatment, but post-treatment, their lateral frontal activity during category-member generation was significantly more right lateralized than that of controls. Patterns of activity pre- and post-treatment suggested increasing efficiency of cortical processing as a result of treatment in the four patients who improved. The one patient who did not improve during treatment showed a leftward shift in lateral frontal lateralization that was significantly different from the four patients who did improve. Neither medial frontal nor posterior perisylvian re-lateralization from immediately pre- to immediately post-treatment images was a necessary condition for significant treatment gains or shift in lateral frontal lateralization. Of the three patients who improved and in whom posterior perisylvian activity could be measured at post-treatment fMRI, all maintained equal or greater amounts of left-hemisphere perisylvian activity as compared to right. This finding is consistent with reviews suggesting both hemispheres are involved in recovery of language in aphasia patients.

Assessment of the Language Laterality Index in Patients with Brain Tumor Using Functional MR Imaging: Effects of Thresholding, Task Selection, and Prior Surgery

BACKGROUND AND PURPOSE: Functional MR imaging (fMRI) is used to determine preoperatively the laterality of cortical language representation along with the relationship of language areas to adjacent brain tumors. The purpose of this study was to determine whether changing the statistical threshold for different language tasks influences the language laterality index (LI) for a group of controls, patients with tumor without prior surgery, and patients with tumor and prior surgery. MATERIALS AND METHODS: Seven controls, 9 patients with tumor without prior surgery, and 4 patients with tumor and prior surgery performed verb-generation, phonemic fluency, and semantic fluency language tasks during fMRI. Interhemispheric activation differences between the left and right Broca regions of interest were determined by calculating language LIs. LIs were compared within each group, between groups, and between language tasks. Intraoperative electrocortical mapping or the presence of aphasia during postoperative neurology examinations or both were used as ground truth. RESULTS: The language LI varied as a result of statistical thresholding, presence of tumor, prior surgery, and language task. Although patients and controls followed a similar shape in the LI curve, there was no optimal P value for determining the LI. Three patients demonstrated a shift in the LI between hemispheres as a function of statistical threshold. Verb generation was the least variable task both between tasks and across groups. CONCLUSION: For preoperative patients with tumor, the LI should be examined across a spectrum of P values and a range of tasks to ensure reliability. Our data suggest that the LI may be threshold- and task-dependent, particularly in the presence of adjacent tumor.

Functional MRI in the brain tumor patient.

Functional magnetic resonance imaging (fMRI) has been adopted almost universally by disciplines that endeavor to understand how the brain works. As basic scientists tune the technique, clinicians are increasingly able to apply brain mapping with fMRI to their clinical practice. We present here a guide to using fMRI in a clinical setting. We discuss the basic considerations of functional brain mapping in patients with brain tumors including: patient screening and training, paradigm design, data analysis and interpretation of the fMRI scans.

A pneumatic vibrotactile stimulation device for fMRI

Mapping the functional response of the somatosensory cortex is useful both for characterizing normal brain activity and for determining the functional integrity of damaged cortex compromised by stroke or other neurological insults. A variety of stimulators have been used to produce somatosensory cortex activation in functional brain imaging, including brushes and swabs operated manually, pneumatically and mechanically powered mechanical vibrators, air puffs, and vibrating ceramic piezoelectric wafers and benders. A closed‐system, pneumatically driven rubber diaphragm is reported that overcomes many of the limitations of existing vibrotactile devices and produces robust sensory cortex activation in an fMRI experiment. Magn Reson Med 51:640–643, 2004.

Somatotopic Organization of Motor Pathways in the Internal Capsule: A Probabilistic Diffusion Tractography Study

BACKGROUND AND PURPOSE: The location of the motor pathways in the PLIC remains controversial. In the current study, we trace the fibers from the tongue, face, hand, and foot motor cortices by using probabilistic diffusion tractography and define their somatotopic organization in the PLIC. MATERIALS AND METHODS: Twenty subjects were retrospectively studied. Fiber tracts were separately calculated between ROIs in the cerebral peduncle and in the 4 different motor regions in the precentral gyrus. Probabilistic connectivity maps were generated, and the voxel with the highest probability was designated as the position of the motor pathway. The PI and LI were defined as the relative anteroposterior and mediolateral locations of the motor pathways. RESULTS: Tongue pathways were located anteromedial to face in 16 hemispheres (40%), with P < .05 for the PI and LI. Face pathways were located anteromedial to hand in 25 hemispheres (62.5%) with P < .05 for PI and LI. Hand pathways were anteromedial to foot in 14 hemispheres (35%) and anterior in 11 hemispheres (27.5%), with P < .05 for PI but P > .13 for LI. Group analysis showed that the somatotopic arrangement of the bilateral hemispheres was symmetric. CONCLUSIONS: Probabilistic tractography demonstrated the anteroposterior alignment of the motor pathways along the long axis in the PLIC. Probabilistic tractography successfully tracked the motor pathways of the tongue, face, hand, and foot from the precentral gyrus through their intersection with the larger superior longitudinal fasciculus to the PLIC in all cases, overcoming limitations of standard (nonprobabilistic) tractography methods.

Cortical activation during swallowing rehabilitation maneuvers: a functional MRI study of healthy controls.

We hypothesize that the central response during swallowing rehabilitation is critical and may be exploited to maximize the therapeutic benefit. We seek to provide preliminary data regarding the neural networks associated with commonly employed rehabilitation strategies to increase our understanding of the neural bases underlying these maneuvers.