Date of Graduation

Winter 12-18-2026

Document Type

Dissertation

Degree Name

Doctor of Psychology in Clinical Psychology (PsyD)

College/School

School of Nursing and Health Professions

Program

Clinical Psychology (PsyD)

First Advisor

Brent Ferm, PhD

Second Advisor

Aoife O'Donovan, PhD

Third Advisor

Susana Fryer. PhD

Abstract

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline, memory impairment, and disruption of neural networks involved in cognitive functioning. Although existing treatments may provide symptomatic benefit, there remains a need for interventions capable of slowing or stabilizing disease progression. Deep brain stimulation (DBS) has emerged as a potential neuromodulatory intervention for early-stage AD through stimulation of memory- and cognition-related neural circuitry. This dissertation employed a systematic review research methodology to examine teh neuropsychological and neurobiological outcomes associated with DBS targeting the fornix (DBS-f) and nucleus basalis of Meynert (DBS-NBM) in individuals with early-stage AD over 12–24 months. The review followed PRISMA and Cochrane guidelines and included eight eligible reports, comprising randomized controlled and open-label investigations; importantly, two DBS-f publications reported outcomes from the same ADvance trial cohort rather than independent participant samples. Cognitive outcomes included measures such as the Alzheimer’s Disease Assessment Scale–Cognitive Subscale (ADAS-Cog), Mini-Mental State Examination (MMSE), and Clinical Dementia Rating Scale (CDR), alongside neurobiological outcomes including cerebral glucose metabolism and cortical thickness. Randomized controlled findings for DBS-f did not demonstrate significant improvements in primary cognitive outcomes compared with sham stimulation, although open-label findings suggested possible stabilization or slowing of cognitive decline in some patients. DBS-NBM findings demonstrated somewhat more consistent evidence of cognitive stabilization, particularly among individuals at earlier stages of disease. Neurobiological findings across both targets included changes in cerebral glucose metabolism and associations between preserved cortical thickness and favorable cognitive outcomes. Overall, cognitive improvements were modest and generally not statistically significant; however, patterns of cognitive stabilization and neurobiological change suggest that DBS may modulate neural processes implicated in AD. Interpretation is limited by small sample sizes, limited statistical power, and the prevalence of non-randomized designs. Larger randomized controlled trials are needed to determine efficacy and identify patient characteristics associated with treatment response.

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