DBS for Cognitive Deficits After Traumatic Brain Injury

Traumatic brain injury (TBI) remains a significant public health issue with an incidence of 55-70 million individuals worldwide. In Canada, TBI leads to 23,000 hospitalizations per year with 8% of individuals succumbing to their injuries. In addition to neurologic deficits, TBI may lead to a spectrum of long-term impairments, including cognitive difficulties (e.g., attention, memory), neurologic symptoms (e.g., headaches, dizziness) and neuropsychiatric sequalae (e.g. anxiety, post-traumatic stress disorder). TBI has also been associated with neurodegenerative disorders, such as chronic traumatic encephalopathy and the development of Alzheimer's-type pathology.

Cognitive rehabilitation programs are important tools for clinical recovery of TBI patients, improving functional outcomes and the quality of life. Some of these strategies are based on the development of compensatory strategies and neuroplasticity. Due to the short liver nature of some of the associated improvements and neuroplastic phenomena, stimulating specific neuronal circuits has been proposed.

To date, class I evidence suggests that cognitive improvement following rehabilitation is more effective than sham treatment. In general, however, cognitive rehabilitation therapy is effective in 80-90% of patients. This means that 10-20% of patients remain severely disabled despite treatment.

Deep Brain Stimulation is a neurosurgical tool that has been widely used for over twenty years. Most of the experience with DBS comes from the movement disorder literature where significant success has been had with the management of disabling Parkinson's Disease (PD) and dystonia. Owing to similar underlying circuitry, and the frequent co-occurrence of psychiatric and neurologic conditions, DBS has been suggested for the management of treatment resistant neuropsychiatric conditions, with some promising results.

To date, clinical studies using DBS following TBI are largely comprised of case reports and small case series. The most common application of invasive neurostimulation has been for the treatment of post-TBI dystonic symptoms and tremor. In addition to motor improvement, Miller et al reported a series of 4 patients who presented an improvement in visuospatial memory following fornix burst stimulation. Zhou et al reported that DBS delivered to the anterior limb of internal capsule and the region of the nucleus accumbens improved post-TBI auditory hallucinations, mood changes, and insomnia in a single female patient. Kuhn et al. reported a patient who had a substantial reduction in post- TBI self-mutilating behavior following posterior hypothalamus stimulation. An improvement in emotional adjustment and functional independence was reported in 4 TBI patients treated with nucleus accumbens DBS.Aside from the cognitive, psychiatric and mood improvements described above, DBS has also been investigated for the recovery of consciousness in patients in minimally conscious states. Out of 10 patients reported in the literature, an improvement was observed in 8 individuals using coma scales and related metrics.

Patients with memory and cognitive deficits following TBI that do not respond to conventional treatments experience a decrease in quality of life. Despite advances in neuroimaging, genetics, pharmacology and psychosocial interventions in the last half century, little progress has been made in altering the natural history of the condition or its outcome.

This study would explore whether a surgical therapy is safe and potentially effective in patients who develop refractory memory and cognitive deficits following TBI. Preclinical studies suggest that DBS may improve memory deficits in TBI models. Moreover, DBS delivered to the fornix has shown promising clinical results in patients with Alzheimer's disease. The main mechanism for the improvements induced by DBS in memory tests is the development of multiple forms of plasticity.