Unraveling the impenetrable nature of amnesia: A new beginning

Abstract

Research into the neural mechanisms putatively mediating memory consolidation (how memories stabilize over time [Ebbinghaus 1885]), has exploded in the last 30 yr, resulting in one Nobel Prize (Kandel 2001). Subfields, such as long-term potentiaton (LTP), are now industries in and of themselves. The term “long-term potentiation” brings up over 7000 hits on PubMed alone. Across all levels of analyses, there has been impressive insights into the mechanisms stabilizing memories. In the typical memory “consolidation” experiment, animals would receive some manipulation such as an injection of a drug that inhibits one of the putative molecular candidates implicated in plasticity. If animals demonstrated intact short-term memory and impaired long-term memory, then this was taken as an operational demonstration that the behavioral impairment was due to an impairment in the consolidation of the memory (Dudai 2004; McGaugh 2004). In addition, the targeted molecular pathway would be added to the list of mechanisms mediating the consolidation/storage of memory. Because of the tremendous success of this field, it might come as a surprise to some scientists that there is any unanswered issue about the nature of amnesia. However, the issue concerning the nature of amnesia was never unanimously resolved. Other interpretations of amnesia were historically put forth describing the impairment as an inability to access an existing memory (e.g., Lewis 1969; Millin et al. 2001). After decades of debate, no resolution to this issue was found. Those that believed amnesia to be an impairment in the ability to retrieve memories went on to propose behavioral theories of memories in which amnesia was the result of an inability to retrieve the memory (e.g., Spear 1973; Lewis 1979; Miller and Marlin 1984). On the other hand, those who proposed that amnesia was an impairment in the storage of the memory went on to lead the physiological field in its search for the molecular and cellar mechanisms mediating memory consolidation (McGaugh 2000). One result of this breakup is that behavioral theories of memory and the physiological view of memory have been divorced for 30 yr. Of course, it is in the field’s best interest to resolve the current conceptual divide on this issue. Any scientific description of a phenomenon needs to explain it across multiple levels of analyses. However, in the area of memory consolidation there is a substantial disconnection between the physiological and the behavioral and cognitive levels of analyses. One hope of this special section is that it will bring as many of the perspectives concerning the nature of amnesia side by side for consideration. It has also brought in perspectives from different levels of analyses. The hope is that this will inspire readers to think of new ways to bridge the different positions and levels of analyses, and thus be instrumental in inserting new momentum into the fundamental question regarding the nature of amnesia. Below are excerpts from the letter of invitation, which was sent to the scientists who contributed to this special section: