brain structures

Description

Brain structures and functions took center stage today! Neurons in our brains talk to each other via networks with clusters of cell bodies (Nuclei — “Gray Matter”) connected by cables (Axons with Myelin Sheath) called “White Matter.” Many types of Glial cells also support neuronal functioning. Beginning with the most ancient part of the brain (Reptilian/Brainstem/Hindbrain), we considered Autonomic responses mediated by the Medulla (breathing, heart rate, etc.); vigor, tone and wakefulness administered to higher brain centers by the Reticular Activating System; and the Cerebellum with its role in fine motor control (you didn’t poke yourself in the eye!) and keeping us anchored in space and time. Rising above our lizard ancestry, the Limbic System, or “Emotional Brain,” was brought into place, with the central role being played by the Hypothalamus. All other Limbic structures vie for influence with the Hypothalamus (tiny but power-packed!) because of its vast power. It facilitates sexual activity, Homeostasis, hunger & satiation, Endocrine functions, and Autonomic Nervous System activity. It even secretes hormones itself! The Thalamus, which sits atop the Hypothalamus, acts as a switching center for most sensory information, and filters out noise when we need to concentrate on a specific task, behavior, or thought pattern. Our “drive for evaluation” (Is it safe to approach you, or should I avoid you?) has also been linked to the Thalamus and comes into play even before the Thinking Brain gets the data. (Clifford Nass, The Man Who Lied to His Laptop, p. 26) The Amygdala processes fear and aggression, while the Hippocampus specializes in learning and memory (autobiographical – this is MY life!). Next, we looked at the Cerebral Cortex with its many Gyri (ridges) and Sulci (valleys) and the role it enacts as the “Thinking Brain.” Why do we and some other higher mammalian species have so much cortical material? One thought is that negotiating complex social networks requires a lot of social intelligence. The geography of the Cortex was cited: Occipital Lobes (Visual Cortex) make sense of what we see, first in breaking down component parts, and then putting together in an entire scene. Parietal Lobes are involved in analysis, coding, storage, and spatial processing ever shuttling data up to the CEO in the Frontal Lobes. The strip of neurons in the anterior section of the Parietal Lobes is known as the Sensory Cortex where all skin-mediated sensations are processed. Dr. Wilder Penfield applied an electrode to different spots in this region and mapped where touch could be experienced. Remember now, we are basically cross-wired (touch electrode to my Left Sensory Cortex that corresponds to my shoulder and it “feels” as if someone touched my right shoulder!). The same is true of Dr. Penfield’s mapping of the Motor Cortex, the strip of neurons in the posterior section of the Frontal Lobes. Apply that electrode to the same spot in my Left Motor Cortex, and my right shoulder will “move!” Although the Temporal Lobes are involved in some other functions (emotion and memory), we emphasized the Auditory component. Sound taken in by the left ear is processed primarily in the Right Auditory (Temporal) Cortex, just as sound taken in by the right ear will be processed in the Left Auditory Cortex. Next came the Frontal Lobes which are responsible for “forming and sustaining intentions, planning actions, and carrying them through.” (Alexandr Luria, The Man With A Shattered World, p. 34) This is where we make moral judgments and formulate abstract thoughts. The Frontal Lobes also carry on a continuous conversation with the Emotional Brain. When the Emotional Brain wants to act impulsively, the Frontal Lobes devise a plan to delay such action. Finally, we honed in on the Left Hemisphere of the brain and its critical role in the “language” function for the vast majority of people. When reading, the Left Hemisphere’s Angular Gyrus puts the words into auditory code (read it to self); then, Wernicke’s Area (Left Temporo-Parieto region) comprehends the material; finally, Broca’s Area (Left Frontal Lobe) speaks the word in coordination with the muscles of speech as governed by the Motor Cortex. We can even take pictures of the functioning brain (in vivo) while a language task is being completed and the Left Hemisphere shows far more activity than the Right Hemisphere! In this week’s online class, we will look at the concept of “visual fields” and the role they played in Roger Sperry’s experimentation with “Split-Brain” patients (Corpus Callosum had been cut). Sperry won the Nobel Prize for his stellar research.