Disorders of learning and memory have a large social and economic impact in today's society. Unfortunately, existing medical treatments have shown limited clinical efficacy or potential for modification of the disease course. Deep brain stimulation is a successful treatment for movement disorders and has shown promise in a variety of other diseases including psychiatric disorders. The authors review the potential of neuromodulation for the treatment of disorders of learning and memory. They briefly discuss learning circuitry and its involvement in Alzheimer disease and traumatic brain injury. They then review the literature supporting various targets for neuromodulation to improve memory in animals and humans. Multiple targets including entorhinal cortex, fornix, nucleus basalis of Meynert, basal ganglia, and pedunculopontine nucleus have shown a promising potential for improving dysfunctional memory by mechanisms such as altering firing patterns in neuronal networks underlying memory and increasing synaptic plasticity and neurogenesis. Significant work remains to be done to translate these findings into durable clinical therapies.
Sarah K. B. Bick and Emad N. Eskandar
John S. Pezaris and Emad N. Eskandar
Common causes of blindness are diseases that affect the ocular structures, such as glaucoma, retinitis pigmentosa, and macular degeneration, rendering the eyes no longer sensitive to light. The visual pathway, however, as a predominantly central structure, is largely spared in these cases. It is thus widely thought that a device-based prosthetic approach to restoration of visual function will be effective and will enjoy similar success as cochlear implants have for restoration of auditory function. In this article the authors review the potential locations for stimulation electrode placement for visual prostheses, assessing the anatomical and functional advantages and disadvantages of each. Of particular interest to the neurosurgical community is placement of deep brain stimulating electrodes in thalamic structures that has shown substantial promise in an animal model. The theory of operation of visual prostheses is discussed, along with a review of the current state of knowledge. Finally, the visual prosthesis is proposed as a model for a general high-fidelity machine-brain interface.
Rollin Hu, Emad Eskandar and Ziv Williams
Deep brain stimulation (DBS) has become an increasingly popular tool for treating a variety of medically refractory neurological and psychiatric disorders such as Parkinson disease, essential tremor, depression, and obsessive-compulsive disorder. Several targets have been identified for ablation or stimulation based on their anatomical location and presumed function. Areas such as the subthalamic nucleus, globus pallidus, and thalamus, for example, are believed to play a key role in motor control and execution, and they are commonly used in the treatment of motor disorders. Limbic structures such as the cingulate cortex and ventral striatum, believed to be important in motivation, emotion, and higher cognition, have also been targeted for treatment of a number of psychiatric disorders. In all of these settings, DBS is largely aimed at addressing the deleterious aspects of these diseases. In Parkinson disease, for example, DBS has been used to reduce rigidity and tremor, whereas in obsessive-compulsive disorder it has been used to limit compulsive behavior. More recently, however, attention has also turned to the potential use of DBS for enhancing or improving otherwise nonpathological aspects of cognitive function. This review explores the potential role of DBS in augmenting memory formation and recall, and the authors discuss recent studies and future trends in this emerging field.
Sameer A. Sheth, Emad N. Eskandar and Mark A. Liker
Emad N. Eskandar
Emad N. Eskandar, Lawrence F. Borges, Ronald F. Budzik Jr., Christopher M. Putman and Christopher S. Ogilvy
Object. Although the pathophysiology of spinal dural arteriovenous fistulas (AVFs) has recently been elucidated, the optimal treatment strategy for these lesions has yet to be defined. Current management techniques include endovascular embolization or microsurgical obliteration.
Methods. The authors reviewed the records and angiograms of all patients with spinal dural AVFs treated at Massachusetts General Hospital over a 6-year period (1992–1998). During this period, it was intended initially to treat all patients with embolization and to reserve surgery for those in whom endovascular treatment failed or in cases in which pretreatment evaluation suggested that endovascular therapy would be ineffective or unsafe.
A total of 26 patients with spinal dural AVFs were treated: there were 22 men and 4 women with a mean age of 65 years (range 39–79 years). Lesions were located in the following areas: five in foramen magnum/cervical, 13 in thoracic, five in lumbar, and three in sacral. Twenty-three (88%) of 26 patients underwent embolization and three (12%) of 23 patients underwent surgery as the primary mode of treatment. Of the 23 patients in whom embolization was performed or attempted, nine (39%) ultimately required surgery. All patients were stabilized or improved following definitive treatment, as assessed by the Aminoff—Logue scores. There was one death secondary to a myocardial infarction.
Conclusions. These data demonstrate that endovascular therapy can be successful as an initial treatment for the majority of patients; however, there is a 39% failure rate, which is not observed following surgical therapy. Once a definitive therapy has been achieved using either technique virtually all patients are either stabilized or improved.
Nir Lipsman and Andres M. Lozano
Report of two cases
Emad N. Eskandar, G. Rees Cosgrove, Leslie A. Shinobu and John B. Penney Jr.
✓ Pallidotomy has become a widely used treatment for medically refractory Parkinson's disease. However, the optimal lesion size and location within the pallidum have not yet been determined, and the role of repeated pallidotomy remains undefined. The authors present two patients who had unsatisfactory results after their first unilateral pallidotomy but attained dramatic and long-lasting improvement with repeated surgery. The results obtained in these cases indicate that patients who have a good clinical outcome initially but relapse rapidly after surgery should be considered for repeated pallidotomy if the initial lesion was not placed in the optimal location.