Anomic aphasia refers to a persistentinability to retrieve correct words, whilst speech fluency and comprehensionare relatively preserved (Dronkers & Baldo, 2010). Whilst there is no concreteagreement on the cause, Papathanasiouand Coppens (2016) havesuggested that anomic aphasia may be associated with lesions affecting the leftangular Gyrus (left ANG). Transcranial magnetic stimulation (TMS)is an advanced non-invasive tool, which utilises an alternating magnetic field,to induce a weak electrical current in the brain via electromagnetic induction (Cowey,2005). When applied appropriately TMS can disrupt the function of a targetcortical region creating a ‘virtual brain lesion’ (Pascual-Leone, 1999). As Papathanasiou and Coppens (2016) have suggested that lesionsin the left ANG may trigger anomic aphasia,it would appear appropriate to utilise TMS to induce a localised virtual brainlesion in the left ANG, in neurotypical participants, in order to decipher theinvolvement of such brain region in Anomic Aphasia. MethodThisstudy aims to decipher whether left ANG plays a functional role in successfulword retrieval, as measured via the Boston Naming Test- Aphasia Short Form Test(BNT- ASFT; del Toro et al., 2011). Protocol Participants will attend one testingsession comprising two phases; the first phase will involve the specific brainregions being located whilst the second will involve TMS stimulation.
The specificbrain region of interest is the left ANG. Additionally, the Supramarginal Gyrus(SMG) will be stimulated to act as a control area. This area was selected as itis located close in proximity to the left ANG however does not play afunctional role in word retrieval. Consequently, comparing the effect of TMSstimulation of this region to the Left ANG will indicate whether the effect isspecific to the focal region or more general area. The left ANG and SMG will belocated utilising MRI and frameless stereotaxy, in which identifiable targetson the participants MRI scan are utilised to locate the target brain regions onthe scalp (Ccni.gla.ac.uk, 2018).
Prior to testing informed consent will beobtained. Participants will then be required to complete a TMS safety screeninganalysis, comprising a 15-question questionnaire (Rossi et al., 2009).Participants who do not meet exclusion criteria will be instructed to removeall metal objects from their upper body and proceed with the study. Oncompletion of the TMS screening the participant will be familiarised with TMSto ensure they do not experiencing any undue anxiety.
Low frequency (1Hz) offline repetitiveTMS (rTMS) delivered using a figure-of-eight coil will be applied at anintensity of 60% to the left ANG for 10 minutes prior to cognitive testing. Atemporal rate of 1 Hz is specified as this rate has been implicated in inducingan inhibitory effect (Fitzgerald, Fountain, & Daskalakis, 2006). Offline rTMS has been utilised as it hasthe capability to induce longer lasting suppression of neural activity (Bolognini & Ro, 2010).Specifically, Udden et al. (2008) have shown that 10 minutes of stimulation at60% intensity affects Left ANG functioning for six minutes. Therefore as the BNT-ASFT can last up to fiveminutes and the Speed and Capacity of Language Processing (SCOLP; Baddeley, Emslie,& Nimmo-Smith, 1992)control task can last up to two minutes the neural activity of the left ANGshould be supressed for the entirety of the test.
Furthermore, afigure-of-eight coil has been selected as it has been shown that such coilsallow for more focused stimulation of the cortical brain region (Ravazzani,Ruohonen, Grandori, & Tognola, 1996). Following the 10-minutes of TMSsimulation participants will be required to complete the BNT- ASFT. Thisrequires participants to name aloud 15 black and white drawings, ranging indifficulty (del Toro et al.
, 2011). A score out of 15 reflecting thenumber of correct names provided will be obtained. Following this theparticipant will then receive a further 10-minutes of TMS simulation to thesame brain region, and afterwards will complete the SCOLP control task.This task will require participants to indicate whether sentences are true orfalse, completing as many out of 100 as possible in two minutes.
A scorereflecting total number of correct sentences completed will be obtained. On completion of both tasks the trialwill then repeated a further two times once whilst TMS was applied to the SMG controlregion and once with no TMS stimulation. Completion of the three trials andtests within each trial will be randomly counterbalanced across participants. AnalysisBased on Papathanasiou and Coppens’ (2016) assumptions one canhypothesise that performanceon the BNT-ASFT will be significantly reduced followingTMS stimulation to the Left ANG compared to no TMS and TMS to the SMG (SeeFigure 1). Furthermore, performance on the SCOLP will be preservedacross all conditions (See Figure 2). The effect of inhibitory TMS on wordretrieval and word comprehension will be analysed via two separate repeatedmeasures Analysis of Variance’s (ANOVA), in which TMS stimulation (WithinSubject-factor with 3 levels: Left ANG, SMG, no TMS) forms the independentvariable and BNT-ASFT score and SCOLP scores forms the dependent variablerespectively.
Figure 1. Means (and Standard Error) of BNT-ASFTscore for TMS stimulation to the Left ANG, SMG and no TMS. Figure 2. Means (and Standard Error) of SCOLP scorefor TMS stimulation to the Left ANG, SMG and no TMS.
This study employs a fixed intensityhowever, it is widely accepted that different individuals respond verydifferently to TMS (Kaminski, Korb, Villringer, & Ott,2011). Therefore, one cannotassume that comparable electrochemical alterations are occurring in allparticipants as a result of the TMS stimulation, thus posing a potentialproblem. The utilisation of individually adapted stimulation intensities basedupon a participant’s motor threshold may control for this confound. Furthermore,non-specific effects, such as sound artefacts and cutaneous artefacts maypotentially confound the results. In order to control for such effects acontrol task and control brain region have been utilised.
However, one cannotbe fully certain that these controls will successfully partial out thenon-specific effects.