MRI neuroimaging: language recovery in adult aphasia due to stroke

Thesis (Ph.D.)--Boston UniversityThis research focuses on the contribution of magnetic resonance imaging (MRI) to understanding recovery and treatment of aphasia in adults who have suffered a stroke. There are three parts. Part 1 presents the feasibility of the application of an overt, picture-naming, functional MRI (fMRI) paradigm to examine neural activity in chronic, nonfluent aphasia (four mild-moderate and one severe nonfluent/global patient). The advantages and disadvantages of an overt, object picture-naming, fMRI block-design paradigm are discussed. An overt naming fMRI design has potential as a method to provide insight into recovery from adult aphasia including plasticity of the brain after left hemisphere stroke and response to treatment. Part 2 uses the overt naming fMRI paradigm to examine changes in neural activity (neural plasticity) after a two-week series of repetitive transcranial magnetic stimulation (rTMS) treatments to improve picture naming in chronic nonfluent aphasia. An overview of rTMS and rationale for use of rTMS as a clinical treatment for aphasia is provided. Patterns of fMRI activation are examined in two patients with chronic nonfluent aphasia following a two-week series of 1 Hz rTMS treatments to suppress the right pars triangularis portion of the right hemisphere, Broca's homologue. One patient responded well, and the other did not. Differences in fMRI activation in response to the rTMS treatment for the two patients may be due to differences in the patients' lesion sites and extent of damage within each lesion site. Part 3 examines the area of the corpus callosum (CC) in 21 chronic nonfluent aphasia patients and 13 ageequivalent controls using structural MRI. Understanding brain morphology and potential atrophy of the CC in chronic stroke patients may shed light on alterations in the interhemispheric dynamics after stroke, especially patterns of brain reorganization during post-stroke language recovery. A decrease in interhemispheric connections has implications for mechanisms of language recovery and potential success with specific treatment methods. Future directions of both structural and functional neuroimaging to study language recovery in adult aphasia are discussed

Speech perception in MRI scanner noise by persons with aphasia

Purpose. To examine reductions in performance on auditory tasks by aphasic and neurologically-intact individuals as a result of concomitant MRI scanner noise. Methods. Four tasks together forming a continuum of linguistic complexity were developed. They included complex-tone pitch discrimination, same/different discrimination of minimal pair syllables, lexical decision, and sentence plausibility. Each task was performed by persons with aphasia (PWA) and by controls. The stimuli were presented in silence and also in the noise recorded from within the bore of a 3T MRI scanner at three signal-to-noise ratios (S/Ns). Results. Across the four tasks, the PWA scored lower than the controls and performance fell as a function of decreased S/N. However, the rate at which performance fell was not different across the two listener groups in any task. Conclusions. Depending upon the relative levels of the signals and noise, the intense noise accompanying MRI scanning has the potential to severely disrupt performance. However, PWA are no more susceptible to the disruptive influence of this noise than are unimpaired individuals usually employed as controls. Thus, fMRI data from aphasic and control individuals may be interpreted without complications associated with large interactions between scanner noise and performance reduction

Brain regions essential for improved lexical access in an aged aphasic patient: a case report

BACKGROUND: The relationship between functional recovery after brain injury and concomitant neuroplastic changes is emphasized in recent research. In the present study we aimed to delineate brain regions essential for language performance in aphasia using functional magnetic resonance imaging and acquisition in a temporal sparse sampling procedure, which allows monitoring of overt verbal responses during scanning. CASE PRESENTATION: An 80-year old patient with chronic aphasia (2 years post-onset) was investigated before and after intensive language training using an overt picture naming task. Differential brain activation in the right inferior frontal gyrus for correct word retrieval and errors was found. Improved language performance following therapy was mirrored by increased fronto-thalamic activation while stability in more general measures of attention/concentration and working memory was assured. Three healthy age-matched control subjects did not show behavioral changes or increased activation when tested repeatedly within the same 2-week time interval. CONCLUSION: The results bear significance in that the changes in brain activation reported can unequivocally be attributed to the short-term training program and a language domain-specific plasticity process. Moreover, it further challenges the claim of a limited recovery potential in chronic aphasia, even at very old age. Delineation of brain regions essential for performance on a single case basis might have major implications for treatment using transcranial magnetic stimulation

The role of the dominant versus the non-dominant hemisphere: an fMRI study of Aphasia recovery following stroke

Background: Speech production is one of the most frequently affected cognitive functions following stroke; however, the neural mechanisms underlying the recovery of speech function are still incompletely understood. Aims: The current study aims to address the differential contributions of the dominant and non-dominant hemispheres in recovery from aphasia following stroke by comparing data from four stroke patients and 12 control participants to assess the patterns of activation during speech production tasks during functional magnetic resonance imaging (fMRI) scanning. Methods & Procedures: Four chronic stroke patients (three left-hemisphere lesion and one right-hemisphere lesion) diagnosed with Broca’s aphasia at the acute phase, but now recovered to near normal speech ability, were tested on speech production tasks (phonemic fluency, categorical fluency and picture naming) whilst undergoing fMRI. These patients were compared with 12 healthy controls undergoing the same procedure. Outcomes & Results: Individual subject analysis showed activation peaks in perilesional areas in three out of four patients. This included one patient with right-hemisphere lesion, who also showed predominant perilesional activation. Group analysis of control participants showed predominately left-hemisphere activation, but not exclusively so. Laterality indexes were calculated and showed predominant left-hemisphere lateralisation in the control group (LI = 0.4). Three out of the four patients showed speech lateralised to the same hemisphere as their lesion and the fourth patient showed speech lateralised to the opposite hemisphere to their lesion. Different speech production tasks resulted in varying lateralisation indices (LIs) within participants. Conclusions: The data suggest that perilesional areas support recovery of speech in the chronic phase post-stroke regardless of the site of the lesion. The study has implications for the understanding of functional recovery as well as for the paradigms used in fMRI to localise speech production areas. Specifically, a variety of speech tasks are required to elicit activation that is representative of the range of cortical involvement in speech in healthy adults and that also allows for accurate reporting of the extent of recovery experienced in patients

Functional Magnetic Resonance Imaging

"Functional Magnetic Resonance Imaging - Advanced Neuroimaging Applications" is a concise book on applied methods of fMRI used in assessment of cognitive functions in brain and neuropsychological evaluation using motor-sensory activities, language, orthographic disabilities in children. The book will serve the purpose of applied neuropsychological evaluation methods in neuropsychological research projects, as well as relatively experienced psychologists and neuroscientists. Chapters are arranged in the order of basic concepts of fMRI and physiological basis of fMRI after event-related stimulus in first two chapters followed by new concepts of fMRI applied in constraint-induced movement therapy; reliability analysis; refractory SMA epilepsy; consciousness states; rule-guided behavioral analysis; orthographic frequency neighbor analysis for phonological activation; and quantitative multimodal spectroscopic fMRI to evaluate different neuropsychological states

Semantic radical consistency and character transparency effects in Chinese: an ERP study

BACKGROUND: This event-related potential (ERP) study aims to investigate the representation and temporal dynamics of Chinese orthography-to-semantics mappings by simultaneously manipulating character transparency and semantic radical consistency. Character components, referred to as radicals, make up the building blocks used dur...postprin

Functional magnetic resonance imaging of recovery from post-stroke aphasia

This thesis presents the design, development and application of a novel overt picture-naming paradigm through a series of exploratory behavioural and imaging experiments. The paradigm is subsequently used in a functional magnetic resonance imaging study of recovery from post-stroke aphasia. The possibility of comparing correct and error naming responses in aphasic patients and unimpaired subjects induced to make errors was investigated and successfully trialled. This research improves on techniques currently favoured in imaging studies to explore the processes involved in functional recovery in a more analytical way. The novel study design provides a new way to interrogate processing involved in the production of aphasic responses. The intentions of this project were to drive the research field of post-stroke aphasia recovery forward by suggesting and applying new methods of using functional imaging to investigate the current pertinent research questions. In addition to this, it was aimed that data collected from participants who have an aphasic deficit, and those with a healthy language system, would be analysed to provide evidence of how a stroke damaged brain may recover functional language. It was hypothesised that results from aphasic patients would show that successful language performance is associated with cortical activation of the patients' normal left hemispheric language areas, around their lesion site. Conversely, the hypotheses state that production of linguistic errors would correlate with an increase in activation in areas of the right hemisphere homologous to the left lateralised fronto-temporal language production network. It was thought that further investigation of successful and unsuccessful language performance in unimpaired speakers would echo this finding. The current debate in this research field centres on the role of the undamaged hemisphere in successful recovery. Five chronic stage aphasics were tested using the developed continuous scanning, event-related paradigm and their correct and error naming trials were compared. Results indicate that recruitment of cortical areas homologous to the stroke lesion can support successful language processing. This is contrary to the theory that disinhibition of non-dominant language areas may contribute to the production of aphasic errors. An investigation of forced errors in unimpaired speakers was also conducted to provide comparisons with the aphasic patient group. Imaging results showed that the naming-to-deadline paradigm used may provide a useful baseline for the normal processes involved in the monitoring and control of task performance