<P> Besides memory, the amygdala also seems to be an important brain region involved in attentional and emotional processes . First, to define attention in cognitive terms, attention is the ability to focus on some stimuli while ignoring others . Thus, the amygdala seems to be an important structure in this ability . Foremost, however, this structure was historically thought to be linked to fear, allowing the individual to take action in response to that fear . However, as time has gone by, researchers such as Pessoa, generalized this concept with help from evidence of EEG recordings, and concluded that the amygdala helps an organism to define a stimulus and therefore respond accordingly . However, when the amygdala was initially thought to be linked to fear, this gave way for research in the amygdala for emotional processes . Kheirbek demonstrated research that the amygdala is involved in emotional processes, in particular the ventral hippocampus . He described the ventral hippocampus as having a role in neurogenesis and the creation of adult - born granule cells (GC). These cells not only were a crucial part of neurogenesis and the strengthening of spatial memory and learning in the hippocampus but also appear to be an essential component in the amygdala . A deficit of these cells, as Pessoa (2009) predicted in his studies, would result in low emotional functioning, leading to high retention rate of mental diseases, such as anxiety disorders . </P> <P> Social processing, specifically the evaluation of faces in social processing, is an area of cognition specific to the amygdala . In a study done by Todorov, fMRI tasks were performed with participants to evaluate whether the amygdala was involved in the general evaluation of faces . After the study, Todorov concluded from his fMRI results that the amygdala did indeed play a key role in the general evaluation of faces . However, in a study performed by researchers Koscik and his team, the trait of trustworthiness was particularly examined in the evaluation of faces . Koscik and his team demonstrated that the amygdala was involved in evaluating the trustworthiness of an individual . They investigated how brain damage to the amygdala played a role in trustworthiness, and found that individuals that suffered damage tended to confuse trust and betrayal, and thus placed trust in those having done them wrong . Furthermore, Rule, along with his colleagues, expanded on the idea of the amygdala in its critique of trustworthiness in others by performing a study in 2009 in which he examined the amygdala's role in evaluating general first impressions and relating them to real - world outcomes . Their study involved first impressions of CEOs . Rule demonstrated that while the amygdala did play a role in the evaluation of trustworthiness, as observed by Koscik in his own research two years later in 2011, the amygdala also played a generalized role in the overall evaluation of first impression of faces . This latter conclusion, along with Todorov's study on the amygdala's role in general evaluations of faces and Koscik's research on trustworthiness and the amygdala, further solidified evidence that the amygdala plays a role in overall social processing . </P> <P> Paul D. MacLean, as part of his triune brain theory, hypothesized that the limbic system is older than other parts of the forebrain, and that it developed to manage circuitry attributed to the fight or flight first identified by Hans Selye in his report of the General Adaptation Syndrome in 1936 . It may be considered a part of survival adaptation in reptiles as well as mammals (including humans). MacLean postulated that the human brain has evolved three components, that evolved successively, with more recent components developing at the top / front . These components are, respectively: </P> <Ol> <Li> The archipallium or primitive ("reptilian") brain, comprising the structures of the brain stem--medulla, pons, cerebellum, mesencephalon, the oldest basal nuclei--the globus pallidus and the olfactory bulbs . </Li> <Li> The paleopallium or intermediate ("old mammalian") brain, comprising the structures of the limbic system . </Li> <Li> The neopallium, also known as the superior or rational ("new mammalian") brain, comprises almost the whole of the hemispheres (made up of a more recent type of cortex, called neocortex) and some subcortical neuronal groups . It corresponds to the brain of the superior mammals, thus including the primates and, as a consequence, the human species . Similar development of the neocortex in mammalian species unrelated to humans and primates has also occurred, for example in cetaceans and elephants; thus the designation of "superior mammals" is not an evolutionary one, as it has occurred independently in different species . The evolution of higher degrees of intelligence is an example of convergent evolution, and is also seen in non-mammals such as birds . </Li> </Ol>

Is the limbic system the oldest part of the brain