A psychological perspective
New neuroscientific findings supporting a more individualised and biopsychosocial formulation of FND have led to a greater understanding of changes in the activity and functional connectivity of multiple brain networks in patients with functional neurological disorder.
Thus, non-invasive brain stimulation techniques may also be an effective therapeutic option for patients with FND (Gonsalvez et al., 2021; Perez et al., 2021). Indeed, neuroscience studies have confirmed that functional neurological symptoms are associated with abnormalities in the activity and functional connectivity of the motor-limbic brain network (e.g. amygdala, insula, supplementary motor area) as well as the right temporoparietal junction (rTPJ; Perez et al., 2021).
Transcranial Magnetic Stimulation (TMS) and Transcranial Direct Current Stimulation (tDCS) are non-invasive techniques that do not require general anaesthesia and have fewer side effects than other brain stimulation techniques. Studies have also found effective modulation of brain domains and associated disturbances and symptoms that are also characteristic of FND (Gonsalvez et al., 2021).
Transcranial magnetic stimulation (TMS)
Transcranial magnetic stimulation is a non-invasive technique that uses an electromagnetic coil to generate electrical activity in targeted brain regions via magnetic pulses. A magnetic coil placed on the scalp delivers a magnetic pulse that can pass through the cranial bone, generating an electric field on entry. The magnitude of the induced electric current is large enough to generate action potentials and painlessly and safely activate brain networks.However, this technique can only reach the superficial part of the brain(Lefaucheur, 2019).
In the scientific literature, TMS has been shown to be effective in treating the following disorders, among others:
depression (Gershon et al., 2003; McNamara et al., 2001; O'Reardon et al., 2007),
bipolar disorder ( Dolberg et al., 2002; McGirr et al., 2016),
Obsessive-compulsive disorder (Carmi et al., 2019; Lusicic et al., 2018),
schizophrenia (Dlabač-de Lange et al., 2010; Haraldsson et al., 2004),
post-traumatic stress disorder (Cirillo et al., 2019; Karsen et al., 2014),
Parkinson's disease (Cantello et al., 2002, Chou et al., 2015),
dystonia (Latorre et al., 2019; Mauroudakis et al., 1994),
tics (Hsu et al., 2018; Steeves et al., 2012)
epilepsy (Bae et al., 2007; Chen et al., 2016; Tassinari et al., 2003)
pain syndromes (Galhardoni et al., 2015; Nardone et al., 2018; Marlow et al., 2013; Yang and Chang, 2020).
TMS security
The most common side effects of repetitive TMS (rTMS) are :
local pain at the site of stimulation (most likely due to stimulation of the superficial nerves and/or facial muscles)
neck pain (due to prolonged awkward positioning)
headache (most likely due to a change in local cerebral blood flow; Loo et al., 2008).
These side-effects are common, but not serious in intensity and will subside over time.
In addition to these side effects, Loo et al. (2008) also report more serious side effects, which are very rare and usually associated with more intensive TMS protocols:
attacks (rTMS providers are trained in first aid for attacks and must follow security protocols),
hearing impairment (patients must wear hearing protection due to the loud sounds produced with each TMS),
psychosis (important to take special care with bipolar disorder).
Transcranial direct current stimulation (tDCS)
Transcranial direct current stimulation (tDCS) is a non-invasive technique that uses a weak direct current delivered to neural tissue to induce changes in cortical activity for several hours after stimulation (Brunoni et al., 2011). The advantages of this technique lie mainly in its cost-effectiveness, its easy portability and its ability to induce physiological effects through functional connectivity areas, with effects lasting even longer than during the stimulation period alone (Jamil and Nitsche, 2017).
tDCS has proven to be effective in treating, among other things:
motor and cognitive domains (working and long-term memory, learning; Jacobson et al., 2012; Schroeder and Plewnia, 2017).
depression (Meron et al., 2015; Palm et al., 2016),
stroke (Marquez et al., 2015; Schlaug and Nair, 2008),
pain (DaSilva et al., 2012; Lefaucheur et al., 2008; Pacheco-Barrios et al., 2020)
emotional regulation (Feeser et al., 2014)
anxiety (Stein et al., 2020).
tDCS security
tDCS is a safe brain stimulation technique. Rare side effects reported in studies:
burns under the electrodes (due to poor performance; Palm et al., 2008)
mania/hypermania (only in patients with unipolar or bipolar disorder; Palm et al., 2015).
Gonsalvez et al, (2021) performed a systematic review of 21 studies that investigated the effectiveness of rTMS and tDCS in the treatment of FND. Interpretation of the results is limited due to:
small samples,
investigations in the different sub-types of the FND,
variability in the design and performance of rTMS and tDCS,
measured outcomes
The efficacy of these techniques thus needs to be further investigated, taking into account the heterogeneity of FND patients, comorbid neuro(psychiatric disorders), the optimality of the stimulation parameters and the need to find a specific subpopulation of FND patients for whom these techniques would be most effective.
Non-invasive brain stimulation techniques and FND
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