Language and Aphasias

Congratulations to Dr. Stephan Nadeau on the publication of “Language and Aphasias,” which was published in the December issue of Behavioral Neurology and Psychiatry.

PURPOSE OF REVIEW This article reveals how it is possible for a brain composed of 100 billion highly interconnected, lipid-encased, reticular electrochemical devices to support complex functions such as language and how language disorders can be understood as a reflection of degradation of one or more domains of knowledge.

RECENT FINDINGS Ongoing research, building on landmark work regarding parallel distributed processing (PDP), provides the basis for understanding cognitive functions as a manifestation of the activity of populations of millions or billions of neurons in various highly interconnected networks. Population encoding networks have the following intrinsic properties that provide an orderly explanation for normal and degraded language: (1) a capacity for settling into stable “attractor” states; (2) processing occurs in and knowledge (long-term memories) is stored in exactly the same network; (3) a capacity for incorporating statistical regularities of experience, frequency, and age of acquisition; (4) support of content-addressable memory; and (5) graceful degradation, such that lesions increase the probability of errors but do not fundamentally transform network operations. Knowledge in parallel distributed processing networks resides in the strength of connections between units (synapses in the brain). Aphasia, whether stemming from stroke or dementing disorders, can be understood in terms of the degradation of one or more domains of knowledge.

SUMMARY Understanding the brain as a population encoding machine incorporating vast interconnectivity provides an orderly explanation for language function, both normal and abnormal.