Deep Brain Stimulation of the Fornix

Deep brain stimulation (DBS) is a technique in which electrodes are surgically implanted in the brain, and electrical impulses are delivered to brain circuits that aren’t functioning properly as a way to help control symptoms of neurological disorders.

DBS is a well-established method for treating movement disorders such as Parkinson’s disease. It is currently being investigated as a treatment for Alzheimer’s disease.

How DBS works

A DBS system includes three components that are surgically implanted. Small holes are drilled through the skull to allow the placement of electrical leads in the brain. A small battery-powered stimulator is implanted under the collarbone. The stimulator is connected to the electrical leads via a wire placed beneath the skin that runs along the neck and behind the ear.

For Alzheimer’s patients, DBS is often targeted to a brain area called the fornix, part of the brain’s memory circuit. The fornix is a bundle of nerve fibers that connects the hippocampus, a part of the brain associated with memory, with other areas of the brain. 

A study in sheep showed that DBS of the fornix stimulated activity in the hippocampus. In a mouse study, researchers found that DBS of the fornix improved the animals’ memory performance in a maze.

DBS in clinical trials

Functional Neuromodulation, a company developing DBS therapies for Alzheimer’s, sponsored a Phase 2 clinical trial (NCT01608061) that began in 2012 and included 42 patients with mild Alzheimer’s disease in the U.S. and Canada.

DBS systems were implanted in all participants. In one group, the systems were turned “on” and electrical impulses were delivered to the participants’ brains. In the comparison group, the systems remained “off.” Results were reported in 2016 in the Journal of Alzheimer’s Disease.

They showed that the surgery and electrical stimulation were safe and well-tolerated. No significant differences were seen between the “on” and “off” groups in terms of participants’ performance on cognitive tests.

Cerebral glucose metabolism, an indicator of brain activity, increased in the “on” group at six months compared to the “off” group, but the difference was not seen at 12 months.

Another Phase 2 trial (NCT03290274) is currently recruiting Alzheimer’s patients at the Hospital San Carlos in Madrid, Spain, for a study of DBS. DBS will be applied to the fornix in three patients. In another three patients, DBS will be used to stimulate a different brain region, the basal nucleus of Meynert. The study will evaluate the safety of DBS and its impact on Alzheimer’s disease progression.

Xuanwu Hospital in Beijing, China, is also recruiting Alzheimer’s patients for a Phase 2 clinical trial (NCT03352739 nicknamed FANTASIA) of DBS of the fornix or the basal nucleus of Meynert. DBS devices will be implanted in most of the participants; in some, the device will be turned on (experimental group), in others, it will remain off (sham group). There will also be a control group that will not receive surgery but will just take donepezil for the duration of the study.

The study will look at participants’ performance on cognitive tests, volume of the hippocampus as assessed by magnetic resonance imaging (MRI), and brain metabolism measured by positron emission tomography (PET).

Functional Neuromodulation has started a Phase 3 trial in up to 210 Alzheimer’s participants ages 65 and older. The study implanted the first participant in September of 2019. Participants will all receive a DBS system targeting the fornix of the brain but a third of the participants won’t have the system turned on until after a year to serve as a control group. The study will monitor the 12-month change from baseline in Integrated Alzheimer’s Disease Rating Scale (iADRS) and the Clinical Dementia Rating Scale – Sum of Boxes (CDR-SOB). The study is expected to be completed in October of 2020.


Last updated: Sept. 30, 2019


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