Lauren L. Cloutman

The variation of function across the human insula mirrors its patterns of structural connectivity: Evidence from in vivo probabilistic tractography

The human insula is a functionally complex yet poorly understood region of the cortex, implicated in a wide range of cognitive, motor, emotion and somatosensory activity. To elucidate the functional role of the insula, the current study used in vivo probabilistic tractography to map the structural connectivity of seven anatomically-defined insular subregions. The connectivity patterns identified reveal two complementary insular networks connected via a dual route architecture, and provide key insights about the neural basis of the numerous functions ascribed to this area. Specifically, anterior-most insular regions were associated with a ventrally-based network involving orbital/inferior frontal and anterior/polar temporal regions, forming part of a key emotional salience and cognitive control network associated with the implementation of goal-directed behavior. The posterior and dorsal-middle insular regions were associated with a network focused on posterior and (to a lesser extent) anterior temporal regions via both dorsal and ventral pathways. This is consistent with the involvement of the insula in sound-to-speech transformations, with an implicated role in the temporal resolution, sequencing, and feedback processes crucial for auditory and motor processing, and the monitoring and adjustment of expressive performance.

Connectivity-based structural and functional parcellation of the human cortex using diffusion imaging and tractography

The parcellation of the cortex via its anatomical properties has been an important research endeavor for over a century. To date, however, a universally accepted parcellation scheme for the human brain still remains elusive. In the current review, we explore the use of in vivo diffusion imaging and white matter tractography as a non-invasive method for the structural and functional parcellation of the human cerebral cortex, discussing the strengths and limitations of the current approaches. Cortical parcellation via white matter connectivity is based on the premise that, as connectional anatomy determines functional organization, it should be possible to segregate functionally-distinct cortical regions by identifying similarities and differences in connectivity profiles. Recent studies have provided initial evidence in support of the efficacy of this connectional parcellation methodology. Such investigations have identified distinct cortical subregions which correlate strongly with functional regions identified via fMRI and meta-analyses. Furthermore, a strong parallel between the cortical regions defined via tractographic and more traditional cytoarchitectonic parcellation methods has been observed. However, the degree of correspondence and relative functional importance of cytoarchitectonic- versus connectivity-derived parcellations still remains unclear. Diffusion tractography remains one of the only methods capable of visualizing the structural networks of the brain in vivo. As such, it is of vital importance to continue to improve the accuracy of the methodology and to extend its potential applications in the study of cognition in neurological health and disease.

Therapy for naming deficits in two variants of primary progressive aphasia

Background: Primary progressive aphasia (PPA) refers to a progressive and selective decline in language due to neurodegenerative disease. There are three variants of PPA, progressive nonfluent aphasia (PNFA), semantic dementia (SD), and logopaenic progressive aphasia (LPA). All variants include impaired object naming, but distinct underlying deficits might interfere with naming. Therefore, individuals with different types of PPA may respond differently to naming therapy. Aims: To identify differences in patterns of success and generalisation in response to the same treatment in patient with LPA and a patient with SD. Furthermore, we wished to identify whether the treatment effect was item specific (trained words) or generalised to untrained words in trained or untrained categories. Methods & Procedures: Participants included an individual with LPA and one with SD. An assessment of lexical processing was administered before and after a naming treatment to assess underlying deficits and generalisation effects. Therapy consisted of a cueing hierarchy treatment. Treatment items consisted of pictured objects in the categories of fruits/vegetables and clothing. Outcomes & Results: Two different patterns of performance were observed. The LPA participant improved in naming of treated items and untreated items in both treated and untreated categories. The participant with SD improved in naming treated items only, but showed less deterioration in untreated items in treated than untreated categories. Conclusions: Individuals with PPA can show improved naming (at least temporarily) with therapy, but generalisation to untrained items may depend on the underlying cause of the naming deficit, which may differ across subtypes.

Ischemia in broca area is associated with broca aphasia more reliably in acute than in chronic stroke.

Background and Purpose— We aimed to determine if ischemia involving Broca area predicts Broca aphasia more reliably in acute or chronic stroke. Methods— We included consecutive right-hand-dominant patients with left hemisphere ischemic stroke (<48 hours from onset for acute stroke or >6 months after stroke for chronic stroke). MRI scans were analyzed for ischemic lesions or hypoperfusion in Broca area (Brodmann areas 44 and 45). Patients were scored on the Western Aphasia Battery to classify aphasia syndromes; &khgr;2 tests were used to identify significant associations. Results— The presence of infarct involving any part of Broca area and the presence of Broca or global aphasia was much stronger in acute (&khgr;2=38.1; df1; P<0.0001) than in chronic stroke (&khgr;2=0.54; df1; P=0.46; not significant). The association between infarct or hypoperfusion covering all of Broca area and the presence of Broca or global aphasia was much stronger in acute (&khgr;2=35.8; df1; P<0.0001) than in chronic stroke (&khgr;2=1.2; df1; p=0.27; not significant). In a subset of 20 patients studied longitudinally, the associations were significant only acutely, not chronically (&khgr;2=20; df1; P<0.0001 vs. &khgr;2=0; df1; p=1; not significant for ischemia involving part of Broca area, and &khgr;2=16.4; df1; P<0.0001 vs &khgr;2=3.2; df1; p=0.08; not significant for ischemia covering all of Broca area). Conclusions— Broca aphasia is more reliably associated with infarct/ hypoperfusion of Broca area in acute stroke. Many chronic stroke patients with damage to part or all of Broca area had neither Broca nor global aphasia. Broca or global aphasia was sometimes present initially in these patients but resolved by 6 months. Our results indicate that the acute aphasia syndrome may allow the clinician to predict the compromised vascular territory, even when structural imaging shows only a small (or no) infarct.

Site of the ischemic penumbra as a predictor of potential for recovery of functions

Background and Purpose: Diffusion–perfusion mismatch has been used to estimate salvageable tissue and predict potential for recovery in acute stroke. Location of the salvageable tissue may be as important as volume or percentage in predicting potential for recovery of specific functions. Impaired naming, a common and disabling deficit after left hemisphere stroke, is often associated with tissue dysfunction of left Brodmann area (BA) 37, posterior inferior temporal cortex. We tested the hypothesis that the presence of diffusion–perfusion mismatch within left BA 37 predicts probability and extent of short-term improvement of naming. Methods: One hundred five patients with acute left hemisphere ischemic stroke had diffusion-weighted imaging, perfusion-weighted imaging, a test of picture naming, and other language tests at admission and 2 to 4 days later. Linear regression was used to determine whether diffusion–perfusion mismatch in any BA in language cortex, total volume of mismatch, or diffusion or perfusion abnormality predicted degree of improvement in naming by days 3 to 5. Results: The presence of >20% diffusion–perfusion mismatch in left BA 37 and total volumes of diffusion and perfusion abnormality at day 1 each independently predicted degree of improvement in naming. Mismatch in this area did not predict the degree of improvement in other language tests or the NIH Stroke Scale in this study. Conclusions/Relevance: Diffusion–perfusion mismatch in left Brodmann area 37 was strongly associated with acute improvement in naming, independently of volume or percentage of total mismatch or diffusion or perfusion abnormality. These data indicate that mismatch in a particular area is a marker of salvageable tissue and an important predictor of potential for recovery of functions that depend on that area. Location of mismatch before treatment may help to predict potential benefits of reperfusion. GLOSSARY: ADC = apparent diffusion coefficient; BA = Brodmann area; DWI = diffusion-weighted imaging; NIHSS = NIH Stroke Scale; PWI = perfusion-weighted imaging; TE = echo time; TR = repetition time; TTP = time to peak.

The tract terminations in the temporal lobe: Their location and associated functions.

Temporal lobe networks are associated with multiple cognitive domains. Despite an upsurge of interest in connectional neuroanatomy, the terminations of the main fibre tracts in the human brain are yet to be mapped. This information is essential given that neurological, neuroanatomical and computational accounts expect neural functions to be strongly shaped by the pattern of white-matter connections. This paper uses a probabilistic tractography approach to identify the main cortical areas that contribute to the major temporal lobe tracts. In order to associate the tract terminations to known functional domains of the temporal lobe, eight automated meta-analyses were performed using the Neurosynth database. Overlaps between the functional regions highlighted by the meta-analyses and the termination maps were identified in order to investigate the functional importance of the tracts of the temporal lobe. The termination maps are made available in the Supplementary Materials of this article for use by researchers in the field.

Taking Sides: An Integrative Review of the Impact of Laterality and Polarity on Efficacy of Therapeutic Transcranial Direct Current Stimulation for Anomia in Chronic Poststroke Aphasia

Anomia is a frequent and persistent symptom of poststroke aphasia, resulting from damage to areas of the brain involved in language production. Cortical neuroplasticity plays a significant role in language recovery following stroke and can be facilitated by behavioral speech and language therapy. Recent research suggests that complementing therapy with neurostimulation techniques may enhance functional gains, even amongst those with chronic aphasia. The current review focuses on the use of transcranial Direct Current Stimulation (tDCS) as an adjunct to naming therapy for individuals with chronic poststroke aphasia. Our survey of the literature indicates that combining therapy with anodal (excitatory) stimulation to the left hemisphere and/or cathodal (inhibitory) stimulation to the right hemisphere can increase both naming accuracy and speed when compared to the effects of therapy alone. However, the benefits of tDCS as a complement to therapy have not been yet systematically investigated with respect to site and polarity of stimulation. Recommendations for future research to help determine optimal protocols for combined therapy and tDCS are outlined.

Using in vivo probabilistic tractography to reveal two segregated dorsal 'language-cognitive' pathways in the human brain.

Highlights • The dorsal stream has been postulated to constitute multiple pathways.• Tractography was used to map the connectivity of regions within the left SMG.• The arcuate fasciculus was subdivided into dorso-dorsal/ventro-dorsal pathways.• The parallel pathways appear to underlie functional heterogeneity within the SMG.

Acute recovery of oral word production following stroke: Patterns of performance as predictors of recovery

Background: Impairments in oral word production are common at the onset of stroke. The identification of factors that predict early recovery has important implications for identifying those at greater risk of continued impaired functioning, and the management of the patients care following discharge. Aims: To identify patterns of performance that are predictors of acute recovery of oral word production abilities following stroke; to identify any association between early and more chronic recovery. Method and procedures:Acute stroke patients were administered oral word production tasks within 1–2 days of hospital admission, with repeat testing by 7 days; a subset of patients had repeat testing between three weeks to one year later. Performance was examined for error rate and type to identify potential predictors of early recovery. Outcome and results: The proportion of circumlocution and no response errors at initial testing were associated with the magnitude of recovery of language functioning within the first week following stroke. Patient characteristics of age and gender were found to have no influence on the degree of early recovery observed. None of the examined factors predicted late recovery. The degree of early recovery was not associated with the degree of later recovery. Conclusions: The current study identified patterns of task performance that increase our understanding of how oral word production recovers following acute stroke. The finding that the degree of early recovery does not predict the degree of later recovery is consistent with the hypothesis that early and late recovery are due to different mechanisms (restored blood flow in acute stroke, and reorganization in later recovery).

A graded tractographic parcellation of the temporal lobe

ABSTRACT The temporal lobe has been implicated in multiple cognitive domains through lesion studies as well as cognitive neuroimaging research. There has been a recent increased interest in the structural and connective architecture that underlies these functions. However there has not yet been a comprehensive exploration of the patterns of connectivity that appear across the temporal lobe. This article uses a data driven, spectral reordering approach in order to understand the general axes of structural connectivity within the temporal lobe. Two important findings emerge from the study. Firstly, the temporal lobes overarching patterns of connectivity are organised along two key structural axes: medial to lateral and anteroventral to posterodorsal, mirroring findings in the functional literature. Secondly, the connective organisation of the temporal lobe is graded and transitional; this is reminiscent of the original work of 19th Century neuroanatomists, who posited the existence of some regions which transitioned between one another in a graded fashion. While regions with unique connectivity exist, the boundaries between these are not always sharp. Instead there are zones of graded connectivity reflecting the influence and overlap of shared connectivity. HIGHLIGHTSA graded parcellation identified changes in connectivity across the temporal lobeConnective organisation of the temporal lobe was graded and transitionalTwo axes of organisation were found: medial‐lateral and anterovental‐posterodorsalWhile regions of distinct connectivity exist, their boundaries are not always sharpZones of graded connectivity exist reflecting influence of shared connectivity