This is the third installment in our brain basics blog. Let’s dive a bit more into structure today and get used to some fundamental parts, their names, and their functions. Remember, knowing the parts will enable you to link them together more effectively to create the integration that is the basis of well-being.
This is the most basic part of the brain, enabling the regulation of physiological processes such as our respiration and heart rate. In this region, too, are areas such as the reticular activating system, which control whether we are awake or asleep. Naturally, injury to this area can put us in a life-threatening situation and put us into a coma. Some researchers also place within the brainstem the important functions of our reaction to threat. These include the four F’s of fight, flight, freeze, and faint.
The brainstem does not work alone, being linked to the limbic area above to assist, for example, in creating our fighting states with limbic anger or fleeing states with limbic fear. Overall, the brainstem works closely with the body as a whole and the brain’s limbic area to create our emotional states. Because the limbic area and the brainstem are physically below the higher cortical region, we call these “sub-cortical” areas.
The limbic area is sometimes called a system, but its boundaries are not so clear, and researchers differ as to which areas are included under this term. Not to over-activate your limbic amygdala, but here are some Greek names we’ll need to have under our belt as we go forward with our discussion.
Amygdala—the famous “emotional” area that is a cluster of neurons in an almond shape that link a range of functions together, including responding directly to perceptual input, filtering incoming data for danger, scanning faces, remembering emotionally arousing events, and embedding traumatic events into memory to avoid trauma in the future. An overactive amygdala can be thought of as “too differentiated” and create anxiety in our lives, that feeling of unspecified concern or dread that may have no thoughts, just a feeling. Trauma can increase amygdala firing and growth.
Hippocampus—the sea-horse shaped memory area that enables us to integrate basic “implicit” memories, such as perceptions and emotions, into more complex “explicit” forms of factual and autobiographical recollections. This integrative area of the brain is harmed with child abuse such that it can become inhibited in its growth or even damaged. This smaller hippocampus can be associated with difficulties in encoding and retrieving memories. The hippocampus is one of the only areas that we know of at this time that can grow new neurons throughout the lifespan. Other regions, including the hippocampus, can grow new synaptic linkages throughout our lives.
Hypothalamus—This is the master neuroendocrine center that regulates our hormonal processes as it works with the pituitary gland in the brain to influence the functioning of the entire body. Involved in the release of cortisol, the stress hormone, this limbic region is a fundamental part of the “HPA” axis—the hypothalamic-pituitary-adrenal (above the kidneys gland) axis that is the core of our response to stress.
Anterior Cingulate—This region is sometimes included in the prefrontal region of the cortex, and it is there where we will discuss this important area that links attention, emotion, body, social function, and even pain perception.
Nucleus Accumbens—This is the region of the brain that is a part of the “reward circuitry” governed by the neurotransmitter, dopamine, which plays an important role in our motivational drive. Some place this region outside the limbic terminology, others call it “limbic”—but whatever ultimate category we place it in, this area shapes our drives to do something rewarding—that feels good—as we secrete dopamine. Excessive drives can be due to an overly entrained nucleus accumbens that has become part of the addiction cycle of behavior or ingestion.
Dorsal Striatum—This is the area that gets you to “do something” ultimately as a habit. When the dorsal striatum becomes excessively differentiated from other regions nearby, repeated behaviors can become on “auto-pilot” as habits hold sway in our lives and we cannot seem to use our conscious minds to stop them. For this, we need to understand how the cortex fits into the picture next.
This is the outer bark of the brain, folded in many “gyri,” with the majority structured with six-layered columns that ultimately are about making maps of various things—from perceptions of the outside world to ideas about the brain and well-being. The cortex naturally has many areas, grouped into a left and right side or hemisphere, and then divided into several lobes. The occipital lobe at the back makes maps of three-dimensional space (usually with our eyesight); the parietal lobe at the upper side has a regional map of the body’s touch receptors; the temporal lobe maps out sound from input from the ears; and the frontal lobe sits toward the front.
The frontal lobe’s back layer is responsible for engaging our motor movement so it is called the “motor strip” of the cortex. Just in front of that area is the “pre-motor strip” which enables us to plan out motor action. And then we arrive at the associational cortex, the front-most region of the frontal lobe of the brain, that enables us to make associations, and includes areas that enable us to think and reason. The front-most front of the brain, the part behind the forehead, is called the “prefrontal cortex.” This area broadly involves the linkage of five differentiated sources of energy and information flow: The cortex, the limbic area, the brainstem, the body-proper, and the world of other brains. Thus the prefrontal cortex is profoundly integrative.
Within the prefrontal cortex (PFC) are several areas. We’ll name them here, but in the next installment, we’ll review them in-depth and see how they interface with the other areas of the brain and body as well.
Dorsolateral Prefrontal Cortex (dlPFC)—This region is sometimes called the dlPFC and is involved in the allocation of attention and thought, and so is thought of (by dlPFC’s of course) as a center of executive function. As a dorsal part of the cortex, it is further away from the more “ventral” areas below, such as the limbic region.
Medial Prefrontal Cortex (mPFC)—This area is involved in self-referential reflection, and has both a ventral area (vmPFC) where emotional processes become linked to self-awareness as well as a more cognitive dorsal region (dmPFC).
Orbitofrontal Cortex (OFC)—Some place this area within the ventromedial PFC, but others see it as distinct and involved in reward and drive, as it is very connected to the limbic areas below.
Ventrolateral Prefrontal Cortex (vlPFC)—This area is closely connected to the limbic area below and is thus involved in the regulation of emotion.
Insular Cortex or Anterior Insula—This area is thought by some to be a part of the ventrolateral prefrontal cortex – and it serves to create awareness of the state of the interior of the body. This “interoception” is crucial for bodily awareness and emotional regulation, and appears to be a gateway for empathy.
Anterior Cingulate—This is the limbic interface with the cortex that works closely with the insula (through neural spindles cells also called “von Economo neurons”) and is directly involved in fundamental processes of our lives: A. Allocation of attention; B. Emotional regulation; C. Pain perception; and D. Social processing. In this way, the integrative cingulate links the social and embodied nature of our mental lives. The anterior cingulate has two relatively distinct regions, the dorsal and the ventral areas. These regions function quite differently in depression and thus may serve unique roles we’ll discuss soon. More to come!
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