Amnesic Syndrome

Abstract Clinical studies of patients with amnesia have inspired decades of research, contributing to the characterization of distinct forms of memory. At the same time, it has become clear that amnesia can result from lesions of a number of brain regions—including but not limited to the medial temporal lobes—that form an integrated neural network subserving memory. This chapter characterizes the amnesic syndrome, including its anatomic correlates and associated pattern of functional impairment. In the domain of anterograde memory, the chapter examines how amnesia impacts the ability to acquire new episodic memories as well as new semantic memories, with an emphasis on the contribution of distinct processes to patients’ performance. In the domain of retrograde memory, the chapter discusses the scope of impairment with regard to the distinction between episodic and semantic memory. The status of implicit memory in amnesia is also briefly reviewed, followed by consideration of impairments in domains other than long-term memory, including perception, short-term memory, and episodic simulation. Next, the chapter discusses the most common neurological etiologies of amnesia, with consideration of the pattern of memory impairment and associated neuropathology. These include stroke, hypoxic–ischemic brain injury, encephalitis, Korsakoff syndrome, and transient global amnesia. For etiologies typically associated with lesions outside or beyond the medial temporal lobe, additional neurocognitive deficits are considered that may be superimposed on the classic presentation of the amnesic syndrome.