Looking Inside the Living Brain: Lesioning studies, Brain Stimulation and Neuroimaging Techniques

Lesioning studies and brain stimulation

Looking Inside the Living Brain

Describe how lesioning studies and brain stimulation are used to study the brain.
• We can study the brain by using lesioning techniques to destroy certain areas of the brain in laboratory animals or by electrically stimulating those areas (ESB).
• We can use case studies of human brain damage to learn about the brain's functions but cannot easily generalize from one case to another.
• rTMS and tDCS are noninvasive methods for stimulating the brain. Compare and contrast neuroimaging techniques for mapping the brain's structure and function.
• Different neuroimaging methods allow scientists to investigate the structure or the function of the living brain.
• The electroencepha lograph allows researchers to look at the electroencephalogram (EEG), or electrical activity of the surface of the brain,through the use of electrodes placed on the scalp that are then amplified and viewed using a computer. ERPs allow researchers to look at the timing and progression of cognitive processes.
• CT scans are computer-aided X-rays of the brain and show the skull and brain structure.
• MRI scans use a magnet ic field, radio pulses, and a computer to give researchers an even more detailed look at the structure of the brain.
• PET scans use a radioact ive sugar injected into the bloodstream to track the activity of brain cells, which is enhanced and ,color­ coded by a computer. SPECT allows for the imaging of brain blood flow.
• fMR I allows researchers to look at the activity of the brain over a time period.
• NIRS use infrared light to measure changes in blood oxygen levels in the brain, reflecting increases and decreases in brain activity.

Identify the different structures of the hindbrain and the function of each.
• The medulla is at the very bottom of the brain and at the top of the spinal column. It controls life-sustaining functions such as breathing and swallowing. The nerves from each side of the body also cross over in this structure to opposite sides.
• The pons is above the medulla and acts as a bridge between the cerebellum and the cerebrum. It influences sleep, dreaming, arousal,and coordinat ion of movement on the left and right sides of the body.
• The reticular formation runs through the medulla and the pons and controls our general level of attention and arousal.
• The cerebellum is found at the base and back of the brain and coordinates fine, rapid motor movement, learned reflexes, posture, and muscle tone. It may also be involved in some cognitive and emotional functions.

Compare and contrast neuroimaging techniques

Identify the structures of the brain that are involved in emotion, learning, memory,and motivation.
• The limbic system consists of the thalamus, hypothalamus, hippocampus , and amygdala.
• The thalamus is the relay station that sends sensory information to the proper areas of the cortex.
• The hypothalamus controls hunger,thirst, sexual behavior, sleeping and waking, and emotions. It also controls the pituitary gland.
• The hippocampus is the part of the brain responsible for the formation of long-term declarative memories.
• The amygdala controls our fear responses and memory of fearful stimuli.
• The cingulate cortex is important in both emotional and cognitive processing.

Identify the parts of the cortex that process the different senses and those that control movement of the body.
• The cortex is the outer covering of the cerebrum and consists of a tightly packed layer of neurons about one-tenth of an inch in thickness. Its wrinkles, or corticalization, allow for greater cortical area and are associated with greater brain complexity.
• The cortex is divided into two cerebral hemispheres connected by a thick band of neural fibers called the corpus callosum.
• The occipital lobes at the back and base of each hemisphere process vision and contain the primary visual cortex.
• The parietal lobes at the top and back of the cortex contain the somatosensory area,which processes our sense of touch temperature, and body position.
• The tempora l lobes contain the primary auditory area and are also involved in understanding language.
• The frontal lobes contain the motor cortex, which controls the voluntary muscles, and are also where all the higher mental functions occur, such as planning, language, and complex decision making.

Recall the function of association areas of the cortex, including those especially crucial for language.
• Association areas of the cortex are found in all the lobes but particularly in the frontal lobes.These areas help people make sense.

Explain why the pituitary gland is known as the "master gland."
• Endocrine glands secrete chemicals called hormones directly into the bloodstream, influencing the activity of the muscles and organs.
• The pituitary gland is found in the brainjust below the hypothalamus.Among its many functions, it helps us conserve water and controls oxytocin, a hormone involved in the onset of labor and lactation. The pituitary also regulates growth hormone and influences the activity of the other glands.

Recall the role of various endocrine glands.
• The pineal gland is also located in the brain. It secretes melatonin, a hormone that regulates the sleep-wake cycle, in response to changes in light.
• The thyro id gland is located inside the neck. It controls metabolism (the burning of energy) by secreting thyroxin.
• The pancreas controls the level of sugar in the blood by secreting insulin and glucagons. Too much insulin produces hypoglycemia, whereas too little causes diabetes .
• The gonads are the ovaries in women and testes in men. They secrete hormones to regulate sexual growth, activity,and reproduction.
• The adrenal glands, one on top of each kidney, control the stress reaction through the adrenal medulla's secretion of epinephrine and norepirnephrine.The adrenal cortex secretes more than 30 different corticoids (hormones), controlling salt intake, stress, and sexual development.