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Yes, I know I'm late - very late. I will try to make up time by getting the next several blogs up one each day.
This is the putative May 16th entry on Emotion. It is the first entry in the "Everything Else" section to the "Function" chapter of The Lab Rats Guide to the Brain. The next two entries will look at "Motivation" from two perspectives: the brain areas which actually provide function with respect to motivation, and the psychological aspects of motivation as it relates to memory and behavior.
In the upcoming sections we will touch a lot more on Psychology as a subset of Neuroscience, rather than the Anatomy and Physiology that has comprised many of the previous blogs. One reason is because many of the topics: Emotion, Motivation, Personality, Consciousness, Intelligence, and Thought have a central, unifying theme: associative memory.
I have mentioned before, and will do so many times in this section that "association" is the unique property of memory that allows us to recall specific information *without* requiring computer-like addressing. Memory is much less like a dictionary - a compendium of isolated facts - and much more like a thesaurus, in which looking up a single word yields many associated words with similar meaning. Thus a writer looking for just the right term is able to "associate" from one word through a chain that results in finding that one right word. Likewise, memory is a chain of associations - a scent invokes a memory of perfume, which recalls a former girlfriend, associated with a favorite song, heard on the radio of your old car, which was totaled when the brakes failed, which reminds you that the safety inspection is due on your current vehicle!
Likewise, emotion is not just one process, attributed to just one location in brain. Early studies revealed that damage to the amygdala, limbic system, frontal lobe or parietal lobe produced a change in personality - and most particularly emotion. While it is true that limbic/prefrontal damage tended to produce severe alteration in emotion "affect" (the emotional content present in facial expression, voice, language and physical interpretation), none of these is truly the *source* of emotion, but merely one of the processing areas.
True emotional processing seems to be in the Parietal Lobe, and as such is related to other sensory association areas of cortex. This leads to the supposition that emotion is in fact a product of associative memory combined with sensory input. In this manner, the primary "sensory" structure for emotion *is* the limbic system, in particular, the amygdala. Amygdala is arguably a component of the hippocampal system for processing of memory, however, what it processes is emotional *content*. It is highly activated by fear and stress; inactivation or damage to the amygdala results in either uncontrolled or absence of a normal fear-response. Likewise damage to other regions of the limbic system (i.e. Medial Septum, the dark spot in the middle above amygdala) can result in uncontrolled anger (or total passivity). However in these cases it appears that the culprit is damage to neurons which secrete neurochemicals that affect the rest of the limbic system and parietal lobe.
Other subjective emotions - like/dislike, love/hate - are largely processed by the Parietal and Frontal Lobes, and fall back into the category of Executive function as described in the March 14th blog. The "ability to feel" emotion is also an Executive Function" and yes, it is tightly tied to memory and association. The emotional deficits resulting from head injury and frontal lobotomy (technically "prefrontal lobotomy" since it disconnects the prefrontal cortex from the rest of the Frontal Lobe) result from the brain areas that serve the "conscious" functions of the brain.
But more on that later, when we discuss personality as part of the "Motivation," "Thought" and "Intelligence" sections of The Lab Rats' Guide to the Brain!