Dissociated repetition deficits in aphasia can reflect flexible interactions between left dorsal and ventral streams and gender-dimorphic architecture of the right dorsal stream

Abstract

Assessment of brain-damaged subjects presenting with dissociated repetition deficits after selective injury to either the left dorsal or ventral auditory pathways can provide further insight on their respective roles in verbal repetition. We evaluated repetition performance and its neural correlates using multimodal imaging (anatomical MRI, DTI, fMRI, and18FDG-PET) in a female patient with transcortical motor aphasia (TCMA) and in a male patient with conduction aphasia (CA) who had small contiguous but non-overlapping left perisylvian infarctions. Repetition in the TCMA patient was fully preserved except for a mild impairment in nonwords and digits, whereas the CA patient had impaired repetition of nonwords, digits and word triplet lists. Sentence repetition was impaired, but he repeated novel sentences significantly better than clichés. The TCMA patient had tissue damage and reduced metabolism in the left sensorimotor cortex and insula. DTI showed damage to the left temporo-frontal and parieto-frontal segments of the arcuate fasciculus (AF) and part of the left ventral stream together with well-developed right dorsal and ventral streams, as has been reported in more than one-third of females. The CA patient had tissue damage and reduced metabolic activity in the left temporoparietal cortex with additional metabolic decrements in the left frontal lobe. DTI showed damage to the left temporo-parietal and temporo-frontal segments of the AF, but the ventral stream was spared. The direct segment of the AF in the right hemisphere was also absent with only vestigial remains of the other dorsal subcomponents present, as is often found in males. fMRI during word and nonword repetition revealed bilateral perisylvian activation in the TCMA patient suggesting recruitment of spared segments of the left dorsal stream and right dorsal stream with propagation of signals to temporal lobe structures suggesting a compensatory reallocation of resources via the ventral streams. The CA patient showed a greater activation of these cortical areas than the TCMA patient, but these changes did not result in normal performance. Repetition of word triplet lists activated bilateral perisylvian cortices in both patients, but activation in the CA patient with very poor performance was restricted to small frontal and posterior temporal foci bilaterally. These findings suggest that dissociated repetition deficits in our cases are probably reliant on flexible interactions between left dorsal stream (spared segments, short tracts remains) and left ventral stream and on gender-dimorphic architecture of the right dorsal stream.

Bilingualism and the severity of poststroke aphasia

“…Repetition is considered to be a multifaceted function and relies on attention, working memory, lexical-semantic, syntactic, and phonological processes. Some studies investigating the neural basis of aphasia underscore the contribution of the right hemisphere and non-damaged arcuate fasciculus to successful repetition (Berthier, Ralph, Pujol, & Green, 2012;Berthier et al, 2013;Rogalsky et al, 2015). Interestingly, in a recent study, increased fractional anisotropy values in the phonological segment of the arcuate fasciculus, as well as a trend toward bilateral structural organization of the arcuate fasciculus was demonstrated in early bilinguals compared to late bilinguals (Hämäläinen, Sairanen, Leminen, & Lehtonen, 2017).…”

Words are not enough: nonword repetition as an indicator of arcuate fasciculus integrity during brain tumor resection

“…36 Classically, AF disruption has been associated with repetition impairment observed in conduction aphasia (CA), and interestingly patient performance in repetition may differ depending on whether they are confronted with words or nonwords. For example, Berthier and colleagues 3 reported on a stroke patient with CA who repeated words normally but could not repeat nonwords. Beforehand, McCarthy and Warrington 27 observed that 2 patients with long segment AF damage and diagnosed CA repeated better if the task required active semantic processing, whereas their passive repetition was hampered.…”

“…Joanna sierpowska, Msc, 1,2 andreu gabarrós, MD, PhD, 3 alejandro Fernandez-coello, MD, 3,4 Àngels camins, MD, 5 sara castañer, MD, 5 Montserrat Juncadella, PhD, 6 Joaquín Morís, PhD, 1,2 and antoni rodríguez-Fornells, PhD 1,2,7 1 Cognition and Brain Plasticity Group, Bellvitge Biomedical Research Institute (IDIBELL), L'Hospitalet de Llobregat; 2 Department of Basic Psychology, Campus Bellvitge, University of Barcelona, L'Hospitalet de Llobregat; 3 Hospital Universitari de Bellvitge, Neurosurgery Section, Campus Bellvitge, University of Barcelona, IDIBELL, L'Hospitalet de Llobregat; 4 CIBER de Bioingeniería, Biomateriales y Nanomedicina; 5 Institut de Diagnòstic per la Imatge, Centre Bellvitge, Hospital Universitari de Bellvitge, L'Hospitalet de Llobregat; 6 Hospital Universitari de Bellvitge, Neurology Section, Campus Bellvitge, University of Barcelona, IDIBELL, L'Hospitalet de Llobregat; and 7 Catalan Institution for Research and Advanced Studies, ICREA, Barcelona, Spain obJective Subcortical electrical stimulation during brain surgery may allow localization of functionally crucial white matter fibers and thus tailoring of the tumor resection according to its functional limits. The arcuate fasciculus (AF) is a white matter bundle connecting frontal, temporal, and parietal cortical areas that is often disrupted by left brain lesions.…”

“…In the present study, nonwords were created using letter substitutions in real words and following Spanish phonotactic constraints, resulting in nonwords that were easy to articulate. Nonwords are considered useful when exploring language mechanisms in patients presenting with syndromes such as poststroke aphasia, 3 primary language impairment, 28 specific language impairment, 9,17 hearing impairments, 21 stuttering, 4 Alzheimer's disease, 31 or semantic dementia. 22 We tested the role and reliability of an NWR task as an indicator of AF integrity in comparison with standard word repetition (WR) and picture-naming tasks.…”

Revealing the dual streams of speech processing

“…citations). Although it has become common practice to explain results of neuroimaging studies of speech processing in the context of dual stream models (16)(17)(18)(19)(20)(21), the specific location and extent of the dorsal and ventral streams involved in speech processing, each of which is a theoretical construct based on either animal data (5) or the combination of lesion and functional neuroimaging data in humans (8), remain elusive.…”