1. Lesion Volumes in Agrammatic Aphasia: The Role of the Posterior Perisylvian Region for Syntactic Processing
Borna Bonakdarpour*†, Sladjana Lukic, Kyla Garibaldi*, Dirk-Bart den Ouden*, Stephen C. Fix*, Cynthia K. Thompson*†‡
*Departments of Communication Sciences & Disorders, †Cognitive Neurology and Alzheimer’s Disease Center and ‡Department of Neurology, Northwestern University, Evanston/Chicago, IL, USA
(Borna Bonakdarpour is currently at University of Arizona Health Sciences Center, Tucson, AZ, USA)
INTRODUCTION
METHODOLOGY
RESULTS
DISCUSSION
Agrammatism is characterized by production and comprehension of syntactically complex sentences as well as verb argument structure production deficits.
Although several studies indicate that frontal brain lesions give rise to agrammatism (Grodzinsky, 2006; Caplan, 2001), others have found lesions extending into posterior regions (Wilson & Saygin, 2004; Caplan et al., 2007).
Recent neuroimaging studies also have implicated the Posterior Perisylvian Network (PPN) for verb argument structure processing (Thompson et al. 2007; Bonakdarpour et al. 2007), including the angular gyrus (AG), supramarginal gyrus (SMG), superior temporal gyrus (STG), and middle temporal gyrus (MTG).
A 3T scanner was used to obtain anatomical T1-weighted scans. Using SPM2 all T1 images were normalized to the Talairach template. To avoid normalization distortion of the lesion a threshold of 125 was set to exclude the lesion.
Lesions were outlined and measured using MRIcro (Rorden & Brett, 2000). Procedures similar to those used by Caplan and colleagues (2007) and Schnurr et al. (2005) were used. Reliability measurements were carried out between two investigators until a reliability of higher than 95% was reached.
Accuracy scores (percent correct) derived from the NAVS were as follows: VNT (29-97); VCT (97-100); ASPT (59-100), SPT (0-91), and SCT (40-97). Significant positive correlations were found between performance on the ASPT and the SPT (r=0.51), and between the ASPT and the SCT (r=0.71).
Recruitment of the posterior perisylvian network (PPN) for aspects of sentence processing, including argument structure processing has been implicated in several studies (Shapiro et al. 1993; McCann and Edwards, 2002; Hadar and Palti 2002; Ben Sachar et al., 2004; Thompson et al. 2007; Bonakdarpour et al. 2007).
Shapiro and colleagues (1990) found that patients with a sparing of tissue in this region showed normal on-line verb argument structure processing. Similarly, Kim & Thompson’s (2004) agrammatic patients with lesions constrained to the frontal region showed good ability to detect argument structure violations in a grammaticality judgement tasks; whereas, McCann and Edwards’ (2002) posteriorly lesioned, Wernicke’s aphasic, patients did not. FMRI studies by Ben Sachar et al. (2004), Thompson et al. (2007), Bonakdarpour et al. (2007), Hadar and Palti (2002) also found activation of the PPN for argument structure processing.
The present data support these findings and extend them to the production domain. Using lesion volumetry, we found that this region, in particular the superior temporal and supramarginal gyri, is associated with argument structure production; that is, when tissue in these regions is damaged, argument structure production is affected. In addition, these regions seem to be implicated in both sentence production and sentence comprehension.
These findings shed light on the role of the posterior perisylvian network for language processing.
The STG, MTG, SMG, AG, IFG and MFG were selected as regions of interest and lesioned tissue in these areas was examined. To do this we first imported the ROIs from the Pick Atlas v2.4 (Maldjian et al. 2003; see Figure 2). Then the volume of the lesion within an ROI was measured. Finally this value was correlated with NAVS test scores using the Pearson test.
Figure 3 . Composite 3D reconstruction of brain lesions for 14 agrammatic aphasic patients showing overlapping areas. Color bar shows degree of overlap with purple being not overlap and red being overlap in all 14 patients.
The mean total lesion size was cc, which translated to 11%-40% (mean=23.24%) loss in the left hemisphere using the Talairach brain template for comparison. Composite maps for all subjects showed a maximum overlap in the perisylvian area, including the STG and inferior SMG and extending to the AG (Figure 3).
Figure 1. Activation for two-argument verbs minus one-argument verbs (blue). Also displayed is activation of two-argument and three-argument verbs compared to one-argument verbs (yellow).
The purpose of this study was to quantify topographic and volumetric aspects of lesions in agrammatic aphasic patients. We tested correlation between the extent of lesioned tissue in several language regions of interest (ROIs) and subtests of the Northwestern Assessment of Verbs and Sentences (NAVS; Thompson, in preparation).
Statistical analyses showed significant negative correlations between lesion volume in the SMG and the ASPT (r=-0.54), SPT (r=-0.60) and SCT (r=-0.62) of the NAVS. Lesion volumes in the STG were similarly correlated with ASPT (r=-0.54) and the SPT (r=-0.55). No significant correlations between the other ROIs and NAVS tests were found.
References
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PARTICIPANTS
Fourteen participants with stroke-induced agrammatic aphasia, with Aphasia Quotients (AQs) of (based on the Western Aphasia Battery (WAB, Kertesz, 1982))
To examine aspects of syntactic processing, participants were administered the NAVS which includes a Verb Naming Test (VNT), Verb Comprehension Test (VCT), Argument Structure Production Test (ASPT), Sentence Production Test (SPT) and Sentence Comprehension Test (SCT).
The VNT, VCT, and ASPT examine verbs by argument structure type; whereas the SPT and SCT test production and comprehension of seven sentence types, including actives and passives, object and subject relative clause structures, object and subject wh-questions, and yes-no questions. R
INFERIOR FRONTAL GYRUS
Figure 2 . Selected regions of interest (ROI) using Pick Atlas. The box to the right displays colors assigned to each ROI. (MFG= Middle Frontal Gyrus; IFG= Inferior Frontal Gyrus; STG= Superior Temporal Gyrus; MTG= Middle Temporal Gyrsu; AG= Angular Gyrus; SMG= Supramarginal Gyrus)
Figure 4 . Scatter diagrams for correlation between percentage SMG and STG tissue loss and NAVS tests. SC=Senternce Comprehension Test; SPT=Sentence Production Test; ASPT=Argument Structure Production Test.