The Amygdala Is Enlarged in Children But Not Adolescents with Autism; the Hippocampus Is Enlarged at All Ages
+ Authors and Institutions at article site. The Journal of Neuroscience, 14 July 2004, 24(28): 6392-6401; doi: 10.1523/JNEUROSCI.1297-04.2004
If the amygdala does develop abnormally in autism, what behavioral symptoms might be expected? The amygdala has been implicated in the mediation of social behavior (Brothers et al., 1990) and many other cognitive processes in humans. These include face processing (Grelotti et al., 2002; Haxby et al., 2002), recognition of emotions (Adolphs, 2002; Adolphs et al., 2003), enhancement of memory for emotionally significant events (Cahill et al., 1995; Canli et al., 2000), and predicting reward values (Gottfried et al., 2003). This has lead some to suggest that the amygdala might be the primary structure responsible for the social impairments in autism (Baron-Cohen et al., 2000). However, studies of human and nonhuman primates with amygdala lesions argue against this conclusion (Amaral et al., 2003). Human patients with Urbach-Wiethe, a disease that results in destruction of the amygdala, do not display core autistic symptomotology. In addition, nonhuman primates that sustained amygdala damage early in development are able to produce species-typical social behaviors (Prather et al., 2001).
The view from our animal studies, which is consistent with human lesion studies, is that dysfunction of the amygdala is not responsible for the core social deficits of autism.
This is a very extensive and well-documented study. Oodles of tech. procedure, but also “readable” if you stick to Introduction, Discussion and Results.
My “takeaway” is that Asperger’s likely undergo differential development: faster / slower rather than “not at all”. The real issue is social “receptivity” – perhaps like acquisition of language, acquisition of “social indoctrination” is possible during a window of time-development. Aspergers may pass through that stage but be genetically and physiologically “unprepared” for such acquisition, or have a brain type that is pre-social (pre-agricultural-urban.)