Introduction: In 1953, neurosurgeon William Beecher Scoville performed a bilateral mesial temporal lobe resection on Henry Molaison, who suffered from epilepsy. The operation was novel as a treatment for epilepsy and had an unexpected consequence: a severe compromise of Molaison’s anterograde memory. In a landmark 1957 publication, Scoville and Brenda Milner, a cognitive neuroscientist who had previously collaborated with well-known epilepsy neurosurgeon Wilder Penfield, concluded that mesial temporal lobe structures, particularly the hippocampi, were integral to the formation of new, recent memories.

Methods: A detailed literature review was performed to obtain details of Molaison's operation and of his contributions to neuroscience and neurosurgery.

Results: Prior to Molaison’s operation, human memory was believed to be a global cerebral process. To the contrary, neuropsychological studies performed on Molaison proved that human memory is comprised of separate processes, each with its own neurological origin. For example, although Molaison’s ability to form new memories was severely impaired, studies showed that his personality and cognition were normal, and he retained the ability to acquire new motor skills. After his death in 2008, Molaison’s brain underwent detailed MRI scanning and was subsequently sliced into 2,401 sections. Histological evaluation of Molaison’s brain further elucidated which mesial temporal lobe structures were preserved or resected in his operation, shedding new light on the neuroanatomic underpinnings of short-term memory.

Conclusions: Scoville regretted Molaison’s surgical outcome and spoke vigorously about the dangers of bilateral mesial temporal lobe surgery. Now, during the planning of a unilateral temporal lobectomy, neurosurgeons ensure the integrity of the contralateral hippocampus using various diagnostic studies, such as the Wada test and functional MRI. This report is the first historical account of Molaison’s case in the neurosurgical literature, serving as a reminder of Molaison’s contributions and of the perils of bilateral mesial temporal lobe surgery.

Patient Care: Neurosurgeon William Scoville regretted Henry Molaison's surgical outcome. This historical vignette will serve as a reminder to neurosurgeons regarding the perils of bilateral mesial temporal lobe surgery.

Learning Objectives: 1. Recognize that neurosurgeon William Scoville's bilateral mesial temporal lobe resection on Henry Molaison rendered him profoundly amnesic 2. Learn about the contributions of Henry Molaison to cognitive neuroscience through his participation in neuropsychological studies for over four decades 3. Caution neurosurgeons regarding the dangers of bilateral mesial temporal lobe injury to short-term memory formation

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