As investigative techniques have advanced, there has also been a significant increase in information regarding the storage and access of semantic memory in the human brain. The initial investigations in this area were limited to lesion studies focusing on delineating the organization of the lexical–semantic system for categories of objects and entities. With the advent of modern neuroimaging and brain activation studies, investigations of semantic processing in normal, healthy individuals have resulted in the shaping of the functional–anatomic architecture of semantic memory for entities (e.g. object, animals, and actions) in the human brain. These advances have led to the maturation of the basic knowledge base to the point that a work dedicated to the neural organization of semantic memory was indicated. Just as in any emerging field, there has been less agreement in some domains than in others, as is evidenced in this book by several alternative accounts for the same general neural instantiation for a specific aspect of semantic memory. It is our belief that we will continue to balance multiple accounts of neural mechanisms and localizations associated with semantic memory, even with refinement in experimental tools. The reasons for this may relate to difficulties inherent in establishing functional–anatomic consistencies in general for semantic memory, aside from broad regions associated with common semantic functions. These reasons include, but are not limited to, individual variations of the anatomic substrates that encode semantic memories, different and ever-changing life experiences (affecting salience for example), the likely existence of multiple neural mechanisms to perform certain semantic functions, variability in the extent of semantic memory recall engaged depending on the task to be performed, and likely a select set of semantic memory instantiations that are common to all humans.
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