Effects of Ketamine on Eye Movements, Perception and Brain Function

Effects of Ketamine on Eye Movements, Perception and Brain Function

In this study, the investigators examine the effects of low-dose ketamine on different oculomotor, perceptual and cognitive functions. They also examine effects on concurrent brain activity using blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI). A sample of N=25 healthy, male participants is required to complete the study. The design is within-subjects, placebo-controlled, double-blind and cross-over. A targeted ketamine level in plasma of 100ng/ml is applied. It is hypothesised that ketamine, compared to placebo, will lead to changes in task performance and brain activity similar to those observed in patients with schizophrenia.

The uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist ketamine has been proposed as a model system of the symptoms of schizophrenia. To complement this model system and to allow neurobiological as well as translational studies, biomarkers are often applied to people under the influence of ketamine. Here, we apply oculomotor, perceptual and cognitive biomarkers to healthy human volunteers whilst they undergo BOLD fMRI at 3 Tesla field strength. We use a counter-balanced, placebo-controlled, double-blind, within-subjects design. A sample of 25 healthy participants is required. Participants will receive intravenous (IV) racemic ketamine (with a 100ng/ml target plasma concentration) on one of two assessment days and they will receive placebo (intravenous saline) on the other assessment day. BOLD fMRI will be carried out on a Siemens Trio scanner at the Life&Brain Centre, Bonn. In addition to brain functional and cognitive, perceptual and oculomotor responses, we will also measure self-ratings of psychosis-like experiences. These will be obtained using the Psychotomimetic States Inventory (PSI; Mason et al 2008).

Inclusion Criteria:

• MRI-suitability
• suitability for video-based combined pupil and corneal reflection (VCPCR) eye-tracking
• good command of German language
• willingness to take part

Exclusion Criteria:

• any current or history of axis I disorder diagnosis as assessed by the Mini-International Neuropsychiatric Interview (M.I.N.I.)
• any neurological conditions and heart conditions
• use of any prescription or non-prescription medication up to one week before participation
• personal history of head-injuries, loss of consciousness, eye surgery or impairment of vision (other than corrective lenses)
• any other relevant medical conditions such as high blood pressure
• positive urine drug test (Drug-Screen Multi "5T", nal von minden GmbH)
• history of drug use or current drug use
• under- or overweight (below 18.5 and above 24.9 body mass index (BMI) values)
• any diagnosis of psychotic disorders among first-degree relatives