The hypothalamus and thalamus Continuing the upwardly-oriented tour of brain structures, there are two important structures that sit above the brain stem. These are the hypothalamus (Figure 2-1b) and thalamus (Figure 2-2a), one of each within each hemisphere of the brain. The hypothalamus sits immediately below the thalamus and controls hormone secretion. The hypothalamus acts as the “director” or “master controller” of hormones in the body and thus it has an impact on a wide range of processes, including sexual development, appetite, stress, and sleep. Attached to the hypothalamus is the pituitary gland , which is an endocrine gland (i.e., a gland that secretes hormones into the bloodstream that direct and control other hormones in the rest of the body in The mammillary bodies and optic chiasm Two small structures called the mammillary bodies are attached to the thalamus, one in each hemisphere (Figures 2-1c, 2-2b). These structures are involved in learning and memory. Near the mammillary bodies is a region of the brain where some The basal ganglia Above and to the sides of the thalamus are the basal ganglia (Figure 2-2a). The basal ganglia are made up of the caudate nucleus, the putamen, two parts of the globus pallidus (which together form the lentiform nucleus), and the subthalamic nucleus; again, one set of these structures resides within each hemisphere of the brain. The basal ganglia are not easy to see in a diagram of the brain; they are buried within the left The limbic system The limbic system is a set of structures that surround the basal ganglia (Figure 2-2b). Major parts of the limbic system are the hippocampus, the amygdala, the stria terminalis (a major connecting structure of the limbic system), septal nuclei, and the cingulate cortex; one of each resides within each hemisphere of the brain. The hippocampus is critical for learning and remembering new information. One of the most famous and tragic cases in neuropsychology involved a 27-year-old man known simply as HM, whose hippocampi were surgically removed in 1953. The experimental surgery was an attempt to control severe epilepsy (Corkin, 2013). Immediately following the surgery and for the rest of his long life (he died at age 82 in December, 2008), HM was not able to form new memories for events that happened after the surgery. This type of memory impairment is called anterograde amnesia . His case sparked a wave of case studies and animal research that led to the discovery that the hippocampi are critical for learning many types of new information (Corkin, 2013; Squire, 1987). The amygdala is an important structure for emotion and motivation. The amygdala processes information about fear and other mostly negative emotions. The amygdala aids in learning The cerebral cortex The tour of neuroanatomy ends at the top, outermost region of the brain. The brain is surrounded by a six-layer sheet of cells called the cerebral cortex . The cortex is folded into gyri (i.e., ridges) and sulci (i.e., valleys) and is divided into four major parts called lobes , which are labeled frontal, temporal, parietal, and occipital (Figure 2-1a). The frontal lobes are the largest and the most recently evolved part of the brain and are believed to be what make humans unique from other species. The frontal lobes are involved in motor movement, emotional regulation, and a complex set of thinking abilities called executive functions . Executive functions involve reasoning, problem-solving, shifting attention, persistence, organization, inhibition, initiation, and emotional control (Scott & Schoenberg, 2011b). Many developmental, neurologic, and psychiatric disorders – including ADHD, autism spectrum disorder, schizophrenia, obsessive- compulsive disorder, and neurocognitive disorder due to Alzheimer’s disease – are believed to disrupt executive functions to some degree.
concert with the hypothalamus). Another structure in this area, the pineal gland , is also an endocrine gland; it is involved in the secretion of melatonin, which plays a role in sleep-wake cycles. The thalamus relays incoming sensory information up to higher parts of the brain and also is involved in the regulation of movement commands from higher brain centers. While the thalamus is sometimes called a “way station” for information that is being shuttled up and down in the brain, this description is too passive; the thalamus also plays important roles in higher- order cognitive and emotional processes, such as memory and emotional responses. optic fibers from either side of the brain cross, called the optic chiasm. The crossing of the fibers allows for the left hemisphere to process information from the right visual field and vice versa, consistent with the contralateral organization of the brain. and right hemispheres. The different parts of the basal ganglia work together to regulate movement, and they also play a role in cognition and emotion. When there is damage to parts of the basal ganglia, the affected person often has deficits in movement, thinking, personality, and emotion regulation (Bostan & Strick, 2018). and memories for events that have emotional significance. For example, people are less likely to remember something that occurred on a random, ordinary day two months ago, whereas they are more likely to remember what they did for their birthday two years ago, or what happened on the day they were married, gave birth, or graduated from high school. Some events can remain vivid in our memories for a lifetime due to their emotional significance. When the amygdala is damaged, persons can lose the ability to experience and identify some negative emotions. This may sound desirable, but negative emotions are critical for survival. For example, without being able to feel afraid or fearful, it is hard to be suspicious of someone else’s motives and it is easy to be taken advantage of or physically harmed. The cingulate gyrus is another part of the limbic system that is involved in attention, memory, and the processing of pain information (Figure 2-2b). For example, the cingulate cortex/ gyrus is thought to guide behavior to match a person’s intentions and goals. It also helps persons to selectively attend to some information or stimuli and to block out distractions. The septal nuclei play a role in processing emotions and behaviors related to reward and reinforcement. The olfactory bulbs process sensory information related to smell and are located just underneath the frontal lobes (Figures 2-1a, 2-1c, 2-2b). Damage to the frontal lobes often is associated with damage to the olfactory bulbs, and persons with frontal lobe damage can have impaired ability to smell. Changes or deficits in this sensory activity can be an important signal, indicating the need for a neuropsychological evaluation. The frontal and parietal lobes are divided by the central sulcus (Figure 2-1a). The region immediately anterior to the central sulcus in the frontal lobes is called the precentral gyrus . This is the home of the primary motor cortex, which executes voluntary motor movements. The region of the brain near the back of the central sulcus in the parietal lobes is called the postcentral gyrus . The postcentral gyrus houses the primary somatosensory cortex, which processes sensations in the body (i.e., soma, from ancient Greek) related to touch.
Page 47
Book Code: SWUS1524
EliteLearning.com/Social-Work
Powered by FlippingBook