The influence of symptom provocation on glutamate in obsessive-compulsive disorder - a functional magnetic resonance spectroscopy study

An obsessive compulsive disorder (OCD) is a neuropsychiatric disorder that is
characterized by obsessive and intrusive thoughts that cause fear or anxiety
(American Psychiatric Association, 2013). To relieve these fears, patients
perform repetitive and ritual behaviors (compulsions). These compulsions
include among others a compulsion to organize, check or clean. The prevalence
of OCD is around 1% in the Netherlands (de Bruijn, Beun, de Graaf, ten Have, &
Denys, 2010) and has a chronic course with only 20% of patients who, despite
current drug and behavioral treatments after 10- 20 years of follow-up
remission (Bloch et al., 2013). These figures support the need for new
effective treatments.
Multiple studies implicate dysfunction of fronto-striatal circuits - which
connects the (pre) frontal cortex to striatal areas - in the pathophysiology of
this disorder, possibly due to an imbalance in the concentration of
neurotransmitters such as dopamine and serotonin (Milad & Rauch , 2012; Perani
et al., 2008; van der Wee et al., 2004). Research in more recent years,
however, shows that dysregulation of glutamate and GABA - the primary exciting
and inhibiting neurotransmitters in the fronto-striatal circuits, and beyond,
such as the visual cortex * also play an important role in the pathophysiology
of disorders within the impulsive compulsive spectrum (Boedhoe et al., 2017;
Moreira et al., 2017; Pittenger, Bloch, & Williams, 2011).
Within the visual cortex, the lateral occipital cortex is one of the areas
where emotionally salient stimuli are processed (Garcia-Garcia et al., 2016;
Kuniecki, Woloszyn, Domagalik, & Pilarczyk, 2018). A recent meta-analysis
showed that this area in OCD patients, compared to healthy controls, is more
strongly activated by OCD-related visual stimuli (Thorsen et al., 2018). The
stronger response to disorder-specific stimuli in OCD patients can possibly be
explained by top-down regulation from the limbic system (Pessoa & Adolphs,
2010; Thorsen et al., 2018; Vuilleumier, 2005). The OCD-related hyperactivation
of the limbic system during symptom provocation and abnormal functional
connectivity between the fronto-striatal circuits and the LOC could be
responsible for this (Moreira et al., 2017; Thorsen et al., 2018). In this way,
the LOC may contribute to the pathophysiological changes seen in OCD.
Despite previous studies showing abnormal activation in the LOC of OCD patients
during symptom provocation, little research has been done into glutamate in the
LOC of OCD patients. The concentration of glutamate can be measured in vivo
using Magnetic Resonance Spectroscopy (MRS) - a Magnetic Resonance Imaging
(MRI) technique based on the magnetic properties of glutamate and other
neurometabolites (Figure 1C). Previous MRS studies in patients with OCD have
shown changes in glutamate concentration in different brain areas compared to
healthy controls (for reviews, see (Brennan, Rauch, Jensen, & Pope, 2013;
Naaijen, Lythgoe, Amiri, Buitelaar , & Glennon, 2015) The direction of the
effect, however, depends on the characteristics of the patient group (medicated
versus non-medicated, duration of disease, etc.).
MRS studies also suggest involvement of GABA - the primary inhibitory
neurotransmitter - in the pathophysiology of OCD (Naaijen et al., 2015). The
number of MRS studies that investigated GABA concentrations is limited,
however, because these were mostly performed on MRI scanners with a field
strength of 3 Tesla or lower, on which the GABA peak in the spectrum is
difficult to distinguish from the surrounding peaks of other neurometabolites.
Another disadvantage of previous "resting-state" MRS studies is that it gives a
static picture of the neurometabolite concentrations, without taking into
account the temporal fluctuations. Functional MRS (fMRS) is a relatively new
technique in which it is possible to determine the neurometabolite fluctuations
(Stanley & Raz, 2018). By having a participant perform a task during scanning,
task-induced fluctuations in neurometabolite concentrations can be measured. It
is also technically possible to simultaneously measure brain activity during
the task by alternating (interleaving) the fMRS sequence with a functional
Magnetic Resonance Imaging (fMRI) sequence that is sensitive to the blood
oxygenation level dependent (BOLD) response ( Bednarik et al., 2015; Ip et al.,
2017; Mangia et al., 2007). In this way, the relationship between task-induced
chemical changes and task-induced activation patterns can be studied (Bednarik
et al., 2015; Ip et al., 2017; Mangia et al). The provocation of symptoms by
means of disorder-specific visual cues while measuring fluctuations in
neurometabolite concentrations can therefore offer important insights into the
neurochemical background of symptom development (Figure 1C). In addition, these
insights can give direction to new pharmacological interventions to normalize
neurotransmitter concentrations.
Recent fMRS studies in the healthy population focus primarily on the visual
cortex because of the robust stimulus-related BOLD effects that are observed
there. the same studies also show a relationship between neurotransmitter
dynamics of glutamate and the BOLD response (Bednarik et al., 2015; Ip et al.,
2017; Mangia et al., 2007). Given this relationship and the findings of the
abnormal activation patterns in the LOC due to OCD-related stimuli, we expect
that offering disorder-relevant visual stimuli in patients with OCD will lead
to a greater increase in glutamate concentrations as well as a greater increase
in brain activity, compared with healthy controls.

The primary goal of this study is to gain insight into the role of glutamate in
the LOC of OCD patients while observing symptom-inducing visual stimuli. This
will be investigated by using fMRS on an ultra-high field strength MRI scanner
(7T). This allows us to measure the concentration of glutamate in the LOC and
how the concentration changes in response to viewing of disorder-relevant
visual stimuli in OCD patients relative to age, gender and training matched
healthy controls. The manufactured fMRS spectra also contain information about
the (fluctuating) concentrations of GABA, the primary inhibitory
neurotransmitter, and other neurometabolites. One of the secondary goals of
this study is therefore to investigate the fluctuation in concentration of
these neurometabolites. By alternating the acquisition of fMRS spectra
(interleaving) with echo-planar imaging (EPI) volumes, the BOLD response - a
proxy for brain activity - can be measured simultaneously while participants
perform a symptom provocation task. The second secondary goal of this study is
therefore to measure symptom provocation-related brain activity in the LOC.
Based on this combined fMRS / fMRI sequence, the relationship between brain
activity and metabolite dynamics in the LOC can also be examined during the
performance of the symptom provocation task.
In addition, using this technique in combination with high-resolution
structural anatomical scans and diffusion tensor imaging (DTI), the
relationship between neurometabolite dynamics and OCD-specific structural
characteristics can also be examined

If patients want to participate, after sending the patient's information letter
and after the relevant reflection period has elapsed, the researcher will
contact the subject to discuss the purpose of the study by telephone and to
answer any questions from the potential participant. An informed consent will
be sent to request permission for an initial screening for MRI
contraindications and the collection of demographic information (Social
history). After successful (pre) screening, participants will be invited to
come to the Spinoza Center in Amsterdam for a clinical evaluation,
neuropsychological examination and the production of brain scans (total
duration of five hours, including one hour of scanning). If possible and
willing, participants from another ongoing study in OCD patients
(NL61982.029.17) will also be invited to participate in the current study. The
clinical scales and neuropsychological tests have been harmonized over these
two studies so that the results can be exchanged. When this happens,
participants would only come to sign informed consent and undergo the scan
(total duration: 75 minutes). During the clinical evaluation, additional
(screening) questionnaires will be filled in / taken that relate to the
severity, duration and development of the OCD symptoms (Yale-Brown Obsessive
Compulsive Scale [Y-BOCS], The Dimensional Yale-Brown Obsessive-Compulsive
Scale [DY-BOCS] and OCD Age of Onset questionnaire). The presence of possible
comorbid psychiatric disorders (Structured Clinical Interview for DSM-5
[SCID-5]), depression (Hamilton Rating Scale for Depression [HAM-D]), Tic
disorder / Gilles de la Tourette will also be examined (Tic form), anxiety
(Hamilton Rating Scale for Anxiety [HAM-A]) or sleep problems (Epworth
sleepiness Scale [ESS] and Pittsburgh Sleep Quality index [PSQI]). In addition,
additional questionnaires will be taken to map out various characteristics of
the participant and to rule out possible contraindications for participation in
the study, including: possible psychological disorders of first-degree family
members (Family History Form), treatment history (Treatment history form) ) and
possible neurological or severe somatic disorders (General Medical history
form).
After successful screening, the study will be continued with the
neuropsychological examination. Three short neuropsychological tasks are
performed on paper to determine cognitive functions (Montreal Cognitive
Screening Assessment [MOCA] and Dutch Reading Proficiency Test for Adults
[NLV]). Participants will then perform three computer tasks that again look at
cognitive functions planning and response inhibition (Tower of London task
[TOL], stop signal task [SST] and Temporal discounting task [ICT]. These
neuropsychiatric tasks are taken to measure the cognitive functioning of
patients and healthy controls (sample description) and to include them as
covariates in the static model Participants will also complete a few
questionnaires to look at: OCD subtype (Obsessive Compulsive Inventory [OCI]),
presence of autism (Autism Spectrum Questionnaire [ASQ]), childhood trauma
(Childhood Trauma Questionnaire [CTQ]), Disgust (Disgust questionnaire), hand
preference (PhenX Hand Dominance index) and insomnia and sleepiness (Pittsburgh
Sleep Quality Index [PSQI] and Epworth Sleepiness Scale [ESS]).
As a final part of the study site, participants will undergo the MRI scans. All
participants will be instructed not to take caffeine or nicotine at least two
hours before the scan so as not to disturb the measurement of neurometabolite
concentrations. Participants are once more screened for possible MRI
contraindications (e.g. metal in the body). The scanning procedure consists of
a T1-weighted structural MRI scan for the individual localization of the LOC,
acquisition of the combined fMRS / fMRI sequence during the performance of the
symptom provocation task ( Protocol Figure 2) and an ultra-high resolution DTI
scan. During the task, participants see photos of objects and situations that
have been selected to provoke OCD symptoms. OCD patients are shown disorder
specific stimuli that are contrasted with neutral stimuli (matched for color
and contrast) plates (Figure 2). These visual stimuli were used earlier during
an emotion regulation study and validated in the context of that study (de Wit
et al. 2015). The photos are projected on a screen behind the 7T MRI scanner
that participants can see through a mirror mounted on the MRI main coil.
Immediately before and after performing the task, the participant will be asked
how serious the symptoms are at that moment (on a scale from 0 to 100,
respectively "very relaxed" to "extremely tense"). To ensure that participants
view the visual stimuli carefully, they will be instructed to respond to each
photo by pressing a button on an MRI-compatible button box in response to
numbers shown at the bottom of every stimulus. Any eye abnormalities can be
corrected by wearing MRI compatible glasses. Participants are instructed to
remain as still as possible during scanning. To further reduce movement
artifacts, the head will be immobilized with soft cushions. The scan protocol
takes around 60 minutes in total.
*

In the context of this study, participants are asked a number of questionnaires
that relate to the severity of the symptoms of OCD, mood (depression and
anxiety) and sleep (problems). Part of these questionnaires can already be
completed at home on paper or online before participants come to the research
center. In addition, five short neuropsychological tests are performed for
brain scan research to measure cognitive functions. Taking these tests and the
questionnaires together take approximately four hours.
The brain scan examination also takes approximately 60 minutes. A number of
different scans will be made during this investigation. With most scans,
participants do not have to do anything except stay still. During a scan,
participants perform a symptom provocation task to elicit OCD symptoms through
visual stimuli related to OCD. Healthy controls perform the same task.
No health risks are expected from participation in this study. This study does
not involve any intervention. We screen for possible causes for damage due to
the magnetic field of the MRI scanner (Appendix A in the research protocol). If
the screening is positive, that particular participant is excluded from
participation. Participants may experience slight dizziness when entering the
scanner room and mild muscle twitching while scanning. This is normal.