A striking feature of the studies that have addressed the measurement of the amygdala is the wide range of volumes encountered, with reports of volumes ranging from 1 to almost 4 cm(3). Another striking feature is the number of discrepancies in the landmarks adopted for manual tracing in magnetic resonance imaging (MRI). The goal of our study was to assess the anatomical volume of the amygdala on the basis of its cytoarchitecture while comparing the differences in age and sex. This study was performed on 21 normal male brains (mean age of 56.8 years) and 9 normal female brains (mean age of 61.2 years). The volume of the amygdala was measured by planimetry of Nissl-stained serial sections using ImageJ software. To address the complexity of the amygdala, we elected to use two types of amygdalar measurement that differ mainly in the definition of anterior pole boundaries. The average size of the classic amygdala was 1.24 cm(3) (S.D.=0.14), while the average size of the amygdala with wider borders was 1.63 cm(3) (S.D.=0.2). No interhemispheric or intersexual differences were observed for either type of amygdalar measurement. Neither sex revealed any statistically important relationship between volume of the amygdala and age. Our study was concerned exclusively with the anatomical volume of the amygdala rather than the MRI volume. Nevertheless, our results may have important implications for MRI studies because as of yet there is no gold standard for manual volumetry of the amygdala.
The limbic system, and in particular the amygdala, have been implicated in autism. The amygdala is a complex structure that in rodents consists of at least 12 different nuclei or subnuclei. A comparative analysis of amygdala neuroanatomy in normal vs. autistic brains would be aided by the availability of molecular markers to unambiguously recognize these different amygdala substructures. Here we report on the development of methods to identify genes enriched in the central, lateral and medial nuclei of the rodent amygdala. Our results suggest that laser-capture microdissection of specific amygdala subnuclei, when combined with linear amplification of cRNA probes for oligonucleotide microarray hybridization, can efficiently identify genes whose expression is confined to these substructures. Importantly, many of these genes were missed in previous gene expression-profiling experiments using whole amygdala tissue. The isolation of human orthologs of these subnucleus-specific genes, and/or the application of these methods directly to human tissue, may provide useful markers for characterizing neuropathological correlates of autism, as well as for identifying molecular differences between normal and autistic brains.
The amygdala is a small, almond-shaped structure located deep within the brain. It plays a key role in processing emotions, particularly fear and aggression. Studies have shown that individuals with larger amygdala tend to exhibit more aggressive behaviors.
While studies have found a correlation between amygdala size and aggression, it is important to note that correlation does not necessarily equal causation. Other factors, such as genetics, environment, and upbringing, can also contribute to aggressive behaviors.
There is some evidence to suggest that males may have slightly larger amygdala compared to females, and this difference may play a role in the higher rates of aggressive behaviors seen in males. However, more research is needed to fully understand the relationship between gender, amygdala size, and aggression.
While the size of the amygdala is largely determined by genetics, studies have shown that it can be influenced by environmental factors and experiences. For example, chronic stress and trauma have been linked to a decrease in amygdala volume, which could potentially lead to changes in aggression levels.
At this time, there is not enough evidence to support the use of amygdala size as a definitive predictor or diagnostic tool for aggression. It is just one of many factors that may contribute to aggressive behaviors, and more research is needed to fully understand its role in this complex relationship.