Enhancing Letter-Speech Sound Learning and Reading Network Activation With Transcranial Electrical Stimulation

This study investigates the effects of transcranial electrical stimulation (tES) on the brain and its potential to enhance reading-related learning. The aim is to identify novel techniques for treating developmental dyslexia, which is a common learning disorder that occurs in childhood and can persist into adulthood. Typically, standard therapy for dyslexia consists of specific reading exercises; however, such training often does not fully remediate the difficulties.

This study, therefore, evaluates how transcranial electrical stimulation may be applied to support learning and ultimately reading. During the stimulation, participants perform an artificial orthography learning task simulating letter-speech sound learning. Whereas previous tES reading studies have focused primarily on behavioral outcomes, the present study additionally measures brain activity using fMRI to elucidate how tES affects neural processing and how these effects may relate to reading abilities.

The knowledge gained from this project is intended to support the future development of transcranial electrical stimulation as an intervention for adults and children with developmental dyslexia.

• Transcranial random noise stimulation (Other): Participants will receive high-frequency tRNS (max. 1.5 mA) applied to the left superior temporal gyrus. A high-definition setup (3x1 electrodes) will be used to achieve more focal stimulation. Stimulation will be applied during an artificial orthography learning task with simultaneous fMRI acquisition.
• Sham Stimulation (Other): Participants will also have electrodes placed on their scalp. The setup is programmed to induce a short ramp-up of the chosen electrical current followed by a ramp-down at the beginning and at the end of the stimulation. In between, no current will be applied. Sham stimulation will be applied during an artificial orthography learning task with simultaneous fMRI acquisition.

Primary outcomes

• Performance in the artificial orthography learning task [At second session, up to 8 weeks after baseline]: Performance on the artificial orthography learning task and the artificial orthography reading fluency test will be compared between the stimulation and sham groups.
• fMRI activation and connectivity during print processing [At baseline (Session 1) and at second session, up to 8 weeks after baseline]: fMRI activation and connectivity of the posterior superior temporal gyrus and other regions of the reading and audiovisual learning networks will be compared before, during and after transcranial electrical stimulation (tES). The fMRI tasks performed in the second session include artificial orthography learning and explicit print processing (lexical decision task), whereas implicit print processing (one-back task) is performed both at baseline and in the second session. These changes in activation and connectivity will be compared between the stimulation group and the sham group.

Secondary outcomes

• fMRI brain activation and connectivity in further fMRI tasks: audiovisual processing and naturalistic movie watching [At baseline (Session 1) and at second session, up to 8 weeks after baseline]: Brain activation and connectivity during further fMRI tasks, namely an audiovisual localizer task and a movie-watching paradigm, will be investigated and compared between the two groups. The audiovisual localizer task focuses on brain activation in reading and audiovisual processing regions, and the movie-watching paradigm on connectivity within the resting-state networks.
• Reading and reading-related behavioral measures [At baseline (Session 1) and at second session, up to 8 weeks after baseline]: Reading and reading-related tasks, such as word and pseudoword reading, will be performed before and after tES to provide a behavioral estimate of reading skills.
• Performance in further cognitive tasks [At baseline (Session 1) and at second session, up to 8 weeks after baseline]: The performance in further cognitive tasks (working memory, attention, rapid automatized naming) will be compared before and after tES.

Sex: All, ages: 18 Years to 35 Years, accepts healthy volunteers

Inclusion Criteria:

* Age 18-35
* All genders
* Written informed consent by the participant
* German speaking (native)
* Right-handed

Exclusion Criteria:

* Diagnoses of neurological disorders, intellectual disabilities, or psychiatric disorders (We do not exclude participants with common comorbidities of dyslexia, specifically dyscalculia, Attention Deficit/Hyperactivity Disorder, or Autism Spectrum Disorders)
* History of any acquired brain damage or evidence of fetal alcohol syndrome
* Hearing problems and vision problems that cannot be corrected
* Inability to follow procedures or understand the instructions given in (Swiss-)German
* Current use of psychoactive medications or substances, or a history of substance abuse that may affect brain function, performance or MRI signal quality
* A nonverbal IQ < 80
* Having previously participated in a transcranial electrical stimulation study
* Knowledge to read or write in a language using foreign letters (i.e., different from the Latin alphabet)
* Contraindications to brain stimulation or MRI, such as: History of epilepsy or severe migraine; Skull breach such as craniotomy; Wearing neurostimulators or cardiac pacemakers; Wearing hearing aid devices or cochlear implants, which are not MR safe; Having metal pieces in their body (e.g., piercings that cannot be removed and contain metal, screws or plates from surgical operations, wounds from metal splinters or similar); Claustrophobia or problems lying in the scanner (e.g., pain, anxiety); Previous surgery on the head or heart; Being pregnant (a pregnancy test will be conducted at the MR center before the measurement if a female participant suspects she might be pregnant or is uncertain about her pregnancy status according to the Swiss Ethics Leitlinie:

https://swissethics.ch/assets/pos_papiere_leitfaden/20110906_kek_mri.pdf); Having problems lying still (strong cold, tremor, etc.); Wearing non-removable dental braces