How does alcohol impair memory?
       During the first half of the 20th century, two theoretical hurdles hampered progress toward an understanding of the mechanisms underlying the effects of alcohol on memory. More recent research has cleared away these hurdles, allowing for tremendous gains in the area during the past 50 years.  The first hurdle concerned scientists' understanding of the functional neuroanatomy of memory. In the 1950s, following observations of the well-known amnesic patient H.M., it became clear that different brain regions are involved in the formation, storage, and retrieval of different types of memory. In 1953, large portions of H.M.'s medial temporal lobes, including most of his hippocampus, were removed in an effort to control intractable seizures (Scoville and Milner 1957). Although the frequency and severity of H.M.'s seizures were significantly reduced by the surgery, it soon became clear that H.M. suffered from a dramatic syndrome of memory impairments. He was still able to learn basic motor skills, keep information active in short-term memory for a few seconds or more if left undistracted, and remember episodes of his life from long ago, but he was unable to form new long-term memories for facts and events. The pattern of H.M.'s impairments also forced a re-examination of models of long-term memory storage. Specifically, although H.M. was able to retrieve long-term memories formed roughly a year or more before his surgery, he could not recall events that transpired within the year preceding his surgery. This strongly suggests that the transfer of information into long-term storage actually takes place over several years, with the hippocampus being necessary for its retrieval for the first year or so.
      Subsequent research with other patients confirmed that the hippocampus, an irregularly shaped structure deep in the forebrain, is critically involved in the formation of memories for events (see figure 2 for a depiction of the brain, with the hippocampus and other relevant structures highlighted). For instance, another patient, known as R.B., suffered from memory impairments similar to H.M.'s following damage limited to a region of the hippocampus called hippocampal area CA1, which contains neurons known as pyramidal cells because of the triangular shape of their cell bodies. The pyramidal cells in CA1 send their signals out from the hippocampus to the neocortex, evolutionarily recent tissue that blankets the brain, surrounding older structures(Zola-Morgan et al.1986). (Neocortex literally means "new bark" or "new covering." When one looks at a picture of the human brain, most of what is visible is neocortex.)