Aphantasia describes a form of neurodiversity in which visual imagery is only partially present or completely absent.
Conditions
Interventions
Group 1: Patients with aphantasia will receive three different, approximately 30-minute tDCS protocols (anodal, cathodal, sham
randomized order of treatments) at an intensity of 1.5mA across three examination days. During this stimulation, the strength of mental visual images and autobiographical memory performance will be te
Sponsors
Universitätsklinikum Bonn
Eligibility
Sex/Gender
All
Age
18 Years to 95 Years
Inclusion criteria
Inclusion criteria: Group-specific inclusion criterion – Aphantasia group: A VVIQ score (Vividness of Visual Imagery Questionnaire, Marks 1973) below 32 out of a possible 80 points indicates the presence of aphantasia, based on general research findings (e.g., Dawes et al., 2020; Monzel et al., 2024), and will therefore be treated as an inclusion criterion for the aphantasia group in this study. The healthy control group is required to achieve a VVIQ score above 32. For individuals with hippocampal lesions, the VVIQ score will be recorded, but this is not relevant for inclusion or exclusion. Group-specific inclusion criterion – Hippocampal Lesions group: 20 individuals with hippocampal lesions, such as mild cognitive impairment due to Alzheimer's disease, a history of limbic encephalitis, a history of ischemia/hypoxemia, or hippocampal tumors. These are confirmed conditions affecting the hippocampus, which may include both functional impairment and morphological changes of the hippocampus. All patients with hippocampal lesions must be capable of providing informed consent. If there is any indication that this capacity is not present, the individual will not be enrolled in the study.
Exclusion criteria
Exclusion criteria: Group-specific exclusion criteria – Aphantasia and Control groups: Neurological, psychiatric, or serious internal medical conditions. MRI exclusion criteria: The following exclusion criteria apply to the MRI examination: cardiac or cranial surgeries, cardiac pacemakers, medication pumps (e.g., insulin pumps), hearing aids, removable dental prosthetics, metal parts in or on the body (e.g., acupuncture needles, artificial joints, vascular prostheses, metal fragments, metal clips, implanted electrodes, permanent makeup), and claustrophobia. All participants interested in taking part in the study will be read a questionnaire containing the relevant inclusion and exclusion criteria. Based on the questionnaire, it can be determined whether interested participants qualify for the study. The exclusion criteria will be reviewed again by a study physician at the DZNE prior to the MRI examination. If sufficient documentation attesting to MRI suitability is provided — such as an implant passport, surgical report, etc. — MRI participation may be approved in collaboration with the DZNE's MRI safety officer. Participants sign and confirm that they meet the above-mentioned criteria in order to proceed with the experiments. The presence of neurological, psychiatric, or serious internal medical conditions is also treated as an exclusion criterion. tDCS stimulation exclusion criteria: In order to participate in transcranial direct current stimulation (tDCS), the following additional exclusion criteria apply: - Skull openings or following cranial trepanation - Not to be used in combination with a defibrillator or high-frequency surgery - Brain stimulator - Implanted intracranial metals (e.g., plates, screws, fragments, ventriculoperitoneal shunt, endoprostheses, etc.) - Skin damage (injuries, scars, psoriasis on the scalp) - Traumatic brain injury involving loss of consciousness, brain surgery, or brain tumors - Pregnancy - If contact with the scalp cannot be established
Design outcomes
Primary
| Measure | Time frame |
|---|---|
| The first main objective of the study is to determine whether cathodal stimulation over the visual cortex has a direct positive effect on visual imagery in people with aphantasia and healthy controls. This will be tested using questionnaires and objective test procedures before the first stimulation and during all three stimulations. Questionnaires: 1. Vividness of Visual Imagery Questionnaire (VVIQ; Marks, 1973) 2. Plymouth Sensory Imagery Questionnaire (PSIQ; Andrade et al., 2014) 3. Survey of Autobiographical Memory” (SAM; Palombo et al., 2013) Objective measurement methods for assessing visual imagery: 1. Binocular Rivalry Task (Pearson et al., 2008) 2. Eye tracking: Measurement of pupil size while imagining previously seen, computerized, bright versus dark stimuli (Kay et al., 2020). | — |
Secondary
| Measure | Time frame |
|---|---|
| The second main objective assesses whether a potentially induced enhancement of visual imagery through tDCS also has a positive effect on autobiographical memory performance in aphantasics and healthy controls. This will be tested using a short version of the "Autobiographical Memory Interview" by Levine et al. (2002). Computerized tests of episodic memory: 1) Verbal recall task of abstract and concrete neutral words, based on Clark et al. (2018) 2) Visual recall task of neutral images. In addition, aphantasics, individuals with hippocampal lesions, and healthy controls will be compared across two different fMRI tasks: 1) a task to assess the processing of visuospatial information 2) a task assessing visuo-spatial mental imagery. | — |
Countries
Germany
Contacts
Public ContactCornelia McCormick
Universitätsklinikum
Outcome results
None listed