ABSTRACT
INTRODUCTIONDBS has recently been introduced as a potential treatment to address memory dysfunction associated with Alzheimer’s disease (AD) and Parkinson’s disease (PD). This possibility was first considered following DBS surgery for morbid obesity in a single patient, during which stimulation of the hypothalamus resulted in unexpected stimulation-evoked memory recall [1]. Given the proximity of the hypothalamus to the fornix, an important structure for memory storage and retrieval, it was hypothesized that the current spread to this structure was responsible for the recall phenomenon. Based on this initial finding, a preliminary safety study was conducted investigating fornix DBS in six patients with mild AD [2], and it was found that they experienced significant slowing in cognitive decline without serious adverse effects. Since then, several clinical studies have contributed to the idea that
DBS for memory enhancement may have potential for slowing the progression of memory loss in both AD and PD [2-4]. These studies and the rationale for targeting the fornix and other structures important to memory in the Papez circuit will be discussed in greater detail in this chapter. Neuroanatomy: The Papez CircuitDBS for memory enhancement has focused on structures that play key roles in memory encoding and retrieval. Several structures within the Papez circuit are of interest, including regions of the medial temporal lobe (MTL), specifically, the hippocampus, entorhinal cortex, and perirhinal cortex. The Papez circuit consists of the hippocampus, fornix, mammillary body, anterior nucleus of the thalamus, cingulate cortex, parahippocampal gyrus, and entorhinal cortex [5]. As seen in Fig. 14.1, it
formation through the ascending fibers of the fimbria before branching out into bilateral projections through the fornix. These fibers terminate in the ipsilateral mammillary body. From there, the tract continues up through the mam-milothalamic tract to the anterior nucleus of the thalamus. It then ascends thought the cingulate gyrus and moving posterior and inferior, through the parahippocampal gyrus, entorhinal cortex, and terminating back in the hippocampal formation.
