Anomic aphasia refers to a persistent
inability to retrieve correct words, whilst speech fluency and comprehension
are relatively preserved (Dronkers & Baldo, 2010). Whilst there is no concrete
agreement on the cause, Papathanasiou
and Coppens (2016) have
suggested that anomic aphasia may be associated with lesions affecting the left
angular 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 target
cortical region creating a ‘virtual brain lesion’ (Pascual-Leone, 1999). As Papathanasiou and Coppens (2016) have suggested that lesions
in the left ANG may trigger anomic aphasia,
it would appear appropriate to utilise TMS to induce a localised virtual brain
lesion in the left ANG, in neurotypical participants, in order to decipher the
involvement of such brain region in Anomic Aphasia.
study aims to decipher whether left ANG plays a functional role in successful
word retrieval, as measured via the Boston Naming Test- Aphasia Short Form Test
(BNT- ASFT; del Toro et al., 2011).
Participants will attend one testing
session comprising two phases; the first phase will involve the specific brain
regions being located whilst the second will involve TMS stimulation. The specific
brain 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 it
is located close in proximity to the left ANG however does not play a
functional role in word retrieval. Consequently, comparing the effect of TMS
stimulation of this region to the Left ANG will indicate whether the effect is
specific to the focal region or more general area. The left ANG and SMG will be
located utilising MRI and frameless stereotaxy, in which identifiable targets
on the participants MRI scan are utilised to locate the target brain regions on
the scalp (Ccni.gla.ac.uk, 2018).
Prior to testing informed consent will be
obtained. Participants will then be required to complete a TMS safety screening
analysis, comprising a 15-question questionnaire (Rossi et al., 2009).
Participants who do not meet exclusion criteria will be instructed to remove
all metal objects from their upper body and proceed with the study. On
completion of the TMS screening the participant will be familiarised with TMS
to ensure they do not experiencing any undue anxiety.
Low frequency (1Hz) offline repetitive
TMS (rTMS) delivered using a figure-of-eight coil will be applied at an
intensity of 60% to the left ANG for 10 minutes prior to cognitive testing. A
temporal rate of 1 Hz is specified as this rate has been implicated in inducing
an inhibitory effect (Fitzgerald, Fountain, & Daskalakis, 2006). Offline rTMS has been utilised as it has
the capability to induce longer lasting suppression of neural activity (Bolognini & Ro, 2010).
Specifically, Udden et al. (2008) have shown that 10 minutes of stimulation at
60% intensity affects Left ANG functioning for six minutes. Therefore as the BNT-ASFT can last up to five
minutes 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 ANG
should be supressed for the entirety of the test. Furthermore, a
figure-of-eight coil has been selected as it has been shown that such coils
allow for more focused stimulation of the cortical brain region (Ravazzani,
Ruohonen, Grandori, & Tognola, 1996).
Following the 10-minutes of TMS
simulation participants will be required to complete the BNT- ASFT. This
requires participants to name aloud 15 black and white drawings, ranging in
difficulty (del Toro et al., 2011). A score out of 15 reflecting the
number of correct names provided will be obtained. Following this the
participant will then receive a further 10-minutes of TMS simulation to the
same brain region, and afterwards will complete the SCOLP control task.
This task will require participants to indicate whether sentences are true or
false, completing as many out of 100 as possible in two minutes. A score
reflecting total number of correct sentences completed will be obtained.
On completion of both tasks the trial
will then repeated a further two times once whilst TMS was applied to the SMG control
region and once with no TMS stimulation. Completion of the three trials and
tests within each trial will be randomly counterbalanced across participants.
Based on Papathanasiou and Coppens’ (2016) assumptions one can
hypothesise that performance
on the BNT-ASFT will be significantly reduced following
TMS stimulation to the Left ANG compared to no TMS and TMS to the SMG (See
Figure 1). Furthermore, performance on the SCOLP will be preserved
across all conditions (See Figure 2).
The effect of inhibitory TMS on word
retrieval and word comprehension will be analysed via two separate repeated
measures Analysis of Variance’s (ANOVA), in which TMS stimulation (Within
Subject-factor with 3 levels: Left ANG, SMG, no TMS) forms the independent
variable and BNT-ASFT score and SCOLP scores forms the dependent variable
Figure 1. Means (and Standard Error) of BNT-ASFT
score for TMS stimulation to the Left ANG, SMG and no TMS.
Figure 2. Means (and Standard Error) of SCOLP score
for TMS stimulation to the Left ANG, SMG and no TMS.
This study employs a fixed intensity
however, it is widely accepted that different individuals respond very
differently to TMS (Kaminski, Korb, Villringer, & Ott,
2011). Therefore, one cannot
assume that comparable electrochemical alterations are occurring in all
participants as a result of the TMS stimulation, thus posing a potential
problem. The utilisation of individually adapted stimulation intensities based
upon a participant’s motor threshold may control for this confound. Furthermore,
non-specific effects, such as sound artefacts and cutaneous artefacts may
potentially confound the results. In order to control for such effects a
control task and control brain region have been utilised. However, one cannot
be fully certain that these controls will successfully partial out the