Understanding Brain Function through Clinical Observations and Neuroimaging Techniques - P, Study notes of Psychology

Download Understanding Brain Function through Clinical Observations and Neuroimaging Techniques - P and more Study notes Psychology in PDF only on Docsity! 1 1 Psychology 105 Dr. Gordon Module #4 “The Brain” 2 A. The brain technologies and mapping • 1. Clinical observations • 2. The “EEG” • 3. Electrical Stimulation of the brain (ESB) • 4. Neuroimaging techniques 3 1. Clinical observations • Our understanding of how the brain functions has depended on the technologies available. For many years, there was not a safe or gentle way to determine the functions of the living brain. However, today our technologies have advanced from simple lesioning (destroying small segments of brain tissue) to various brain imaging strategies. The earliest scientific discoveries concerning brain function came from clinical observations. Clinical observations helped Paul Broca discover language centers of the brain. 4 1. Clinical observations • As noted by Myers, clinical observation is one of the oldest methods used to understand brain function. The slide below shows a German soldier during World War II. The design of the German helmet was the result of clinical observations of brain function. During World War I, German neuroscientists observed that visual problems were connected to wounds in the back of the brain. As a result, the helmet was designed to extend backward so the back of the head was fully covered. 5 2. The “EEG” • The electroencephalograph or EEG is a technology that monitors brain function by amplifying electrical wave activity across the surface of the brain. Myers compares the EEG to listening to the hum of a car’s motor underneath the hood. 6 2. The “EEG” • The utility of an EEG is evident when detecting possible impairments in brain functioning. This occurs by presenting a subject a repeated stimulus and then observing electrical recordings to see if that particular brain region is active. For example, if presented a visual stimulus but a subject’s visual cortex does not evoke electrical wave activity, the neuroscientist can suspect brain damage. 7 3. Electrical Stimulation of the brain (ESB) • Electrical stimulation of the brain (ESB) is about sending a weak electrical current into a specific brain structure. ESB is an effective technique because it does not destroy brain tissue. The benefit of ESB is that it assists neuroscientists in establishing important brain and behavior relationships. 8 4. “Neuroimaging” Techniques • For years, the EEG was most common technology used to assess brain dysfunction. Within the last 40 years, neuroimaging has become the standard for assessing brain impairments. A number of them have been developed and include a positron emission tomography (PET scan), computer tomography scan (CT scan), and Magnetic resonance imaging (MRI). We have come a long way since lesioning (destroying brain tissue) and ablations (removing brain tissue). 9 4. “Neuroimaging” Techniques 2 • A PET scan reveals brain dysfunction by generating a “visual display of brain activity that detects where a radioactive glucose goes while the brain performs a given task. The slide above reveals four cortical areas that are responsible for four different functions. The orange areas indicate that glucose hungry neurons are active. One can recognize that thinking requires activity in the frontal lobe while seeing is active at back of the brain. 10 4. “Neuroimaging” Techniques • This technology produces computer enhanced images of the brain. It is essentially a series of x-rays showing photographic slices of the brain. 11 4. “Neuroimaging” Techniques • This technology uses magnetic fields instead of x rays to produce highly detailed images of brain tissue that have far greater clarity and resolution than CAT scans. This is an exciting technology because it yields information about brain structure and function. The MRI can distinguish brain areas as small as 1 to 2 millimeters. 12 B. Lower level brain (Brainstem) • 1. Medulla • 2. Pons • 3. Cerbellum • 4. Reticular formation 13 1. Lower Brain centers: Medulla • The cartoon to the left addresses evolution and the brain. A lower species such as a reptile does not have the neurological development of other higher order organisms. However, lower brain subcortical structures like the medulla, pons, cerebellum, and reticular formation are well developed in lower species. Let’s start with the medulla. 14 1. Lower Brain centers: Medulla • The medulla controls vital cardiovascular and respiratory functions. We cannot survive without the medulla. If the medulla is damage, death is immediate. 15 1. Lower Brain centers: Medulla • The slide above provides a posterior view of the medulla with other brain stem structures. When one breaks a neck at the cervical level, a severed medulla can be fatal. 16 2. Lower Brain centers: Pons • The pons bridges the brainstem and cerebellum. It regulates sleep and arousal. 17 3. Lower Brain centers: Cerebellum • The cerebellum or “little brain” is involved in the coordination of complex movement. A concert pianist’s ability to play would be severely compromised if one’s cerebellum was damaged. 18 3. Lower Brain centers: Cerebellum • Which of the following organisms has the most developed cerebellum? Is it a A) Human being, B) Cat, C) Dog, or D) Any Bird? 19 4. Lower Brain..: Reticular formation • The brainstem and midbrain share structure called the reticular formation. It would appear that the reticular formation has multiple functions. 20 4. Lower Brain..: Reticular formation 5 • The occipital lobe (green) is associated with visual processing. The frontal lobe (yellow) is associated with executive processing (thought, language, problem solving, etc…). The parietal lobe (pink) has been linked to sensory and somatic processing. The temporal lobe (gray) is associated with auditory processing. 41 3. The cortex: Sensory and Motor functions • The fine art of taking notes during a psychology 105 lecture involves every lobe to the left. The temporal lobe translates auditory sounds into receptive language. The frontal lobe involves processing a sequence of words in grammatical order. The parietal lobe allows us to feel the pen. The motor cortex (posterior frontal lobe) takes the integration of inputs above and executes them into a behavioral pattern. Lastly, the occipital lobe allows one to recognize the words one has written. 42 3. The cortex: Sensory and Motor functions • The slide to the left illustrates the motor cortex. This strip of neural tissue is located at the posterior end of the frontal lobe. The slide shows the work of Foerster and Penfield. In separate efforts, these neurosurgeons stimulated areas of the motor cortex and traced specific movements of the body. The result was a mapping of the cortex shown to the left. 43 3. The cortex: Sensory and Motor functions • The “Far Side” cartoon to the left directs humor at the old Penfield studies. Myers cites the research of Nicolelis and Chapin who found that neural impulses originating in the motor cortex were recorded and coverted to computer software patterns. 44 3. The cortex: Sensory and Motor functions • What about Nicolelis and Chapin’s work and human beings? According to Elizabeth Svoboda, neuroscientists like Philip Kennedy have developed technologies that assist quadriplegics control a computer cursor and communicate with their thoughts. An electrode (left) is surgically implanted into the patient's motor cortex, the electrical inputs are monitored and converted to software commands. 45 3. The cortex: Sensory and Motor functions • Through trial and error, patients think about executing movements and watch how thoughts affect the cursor. Subjects learn to connect thoughts with cursor movements. This technology is wireless. Interestingly, at this time, Svoboda reporsts that six people have tried the $100,000 Brain Communicator. Implications from these studies suggest that we can control machines with our thoughts that carry out our motor plans. 46 3. The cortex: Sensory and Motor functions • The somatosensory cortex is a band of fibers that receives neural signals from different areas of the body. The somatosensory cortex is located at the anterior region of the parietal lobe. According to Myers, “the more sensitive a body region, the greater the area of the sensory cortex devoted to it.” 47 4. Association Cortex • Association cortex refers to “areas of the cerebral cortex that are not involved in primary motor or sensory functions.” The neurological comparisons between human beings and other organisms have been discussed. The slide below illustrates the proportion of association cortex as it relates to different organisms. As seen below, human beings have significantly more association cortex than other organisms because of their higher cognitive processes. Other organisms tend to “load up” on sensory and motor cortex. 48 4. Association Cortex • Association cortex disconfirms the psychological myth that we use only 10 percent of our brain. Penfield found that when stimulating various areas of the association cortex, patients would report sensory integrated memories. As Myers notes, “the association areas interpret, integrate, and act on information processed by the sensory areas.” 49 5. What makes our cortex unique (Language)? • Neuroscientists have always been fascinated by the brain’s connection with language. In your text, Myers provides a brief history of the neurological findings related to language. In 1865, Paul Broca, a French neurosurgeon, discovered that the anterior area of the frontal lobe contained the speech center. In doing so, he found the source of a severe speech disorder that was later called “Broca’s aphasia.” This research indicated that the frontal lobe was connected to language function. 50 5. What makes our cortex unique (Language)? • In 1861, Broca treated a 51 year old man named Leborgne, who was given the nickname “Tan” because this was the only syllable he could pronounce. After Tan died of an infection, Broca performed an autopsy 6 and found damage to a small area of the left prefrontal lobe. Broca concluded that this area controlled speech. Tan’s speech disorder is now called Broca’s aphasia. In Greek, aphasia means speechless. 51 5. What makes our cortex unique (Language)? • Broca’s aphasia manifested itself in different ways. For example, in many aphasic cases, persons could speak but not arrange their words to make sense. On the extreme end, as the brain damage extended toward the motor cortex, the aphasic could not arrange words and produce meaningful sounds. 52 5. What makes our cortex unique (Language)? • After Broca’s discovery, the left prefrontal lobe became the focus of language processing. Almost a decade later, another neuroscientist, Carl Wernike, found that language extended to the left temporal lobe. Wernike found that persons with damage to the left temporal lobe had difficulty comprehending speech. This was later termed Wernike’s aphasia. 53 5. What makes our cortex unique (Language)? • According to Myers, a third development in language processing and neuroscience came with the discovery of the angular gyrus. This structure translates visual representations into an auditory codes. Lastly, neuroscientists discovered that Broca’s area, Wernicke’s area, the angular gyrus, motor cortex are connected. It suggests that complex functions require an intricate coordination of different brain areas. 54 6. Brain reorganization (Plasticitty) • Plasticity refers to the brain’s capacity to compensate for the loss of brain tissue through injury or surgery. A young brain (above) is a plastic brain or one that can be molded. When brain tissue is damaged, intact areas assume function for the damaged areas. For example, Myers notes when reading Braille, neural networks of blind persons’ visual cortexes assume function. Documented cases shows miraculous recoveries because of brain plasticity. 55 7. Splitting the Brain • Looking downward on the cerebral cortex, one realizes that it represents two complementary halves known as cerebral hemispheres. We have already surmised that language is located in the left hemisphere. Damage to the left hemisphere also resulted in problems in analytical and abstract reasoning. The right hemisphere seldom led to such dramatic effects. Throughout the years, these findings implied that the left hemisphere was dominant. 56 7. Splitting the Brain • In search of treatment for the severe epileptic, Vogel and Bogen conjectured that the intensity of a seizure could be reduced if abnormal brain activity could be restricted to one hemisphere. As a result, a controversial surgical technique was proposed that would involved cutting the corpus callosum. The corpus callosum is thick band of neural fibers that connects the hemispheres and integrates information between the hemispheres. 57 7. Splitting the Brain • Roger Sperry, pictured to the left, performed preliminary split brain research on other organisms to ensure that the procedure was safe for human beings. The aftermath of split brain procedures is all but history. Vogel and Bogen’s patients appeared normal but under certain experimental conditions, split brain patients revealed some extraordinary tendencies. It was like split brain patient had two personalities. As noted by Myers, the hemipsheres were like a biological odd couple. 58 7. Splitting the Brain • Sperry and colleagues developed split brain protocols that isolated visual information in each hemisphere. The slide to the left illustrates the “information highway from eye to brain.” Information isolated in the right hemisphere was interpreted as nonverbal. In contrast, information isolated in the left hemisphere was interpreted as verbal. In the example to the left, the split brain subject would verbalize an apple but could draw a picture of the pencil with one’s left hand. 59 7. Splitting the Brain • The standard split brain task is presented above. The subject focuses on a dot so information can be isolated to one hemisphere or another. The right hemisphere saw “he” in the left visual field while the left hemisphere saw “art” from right visual field. When asked to report verbally or nonverbally (pointing), subjects act like they processed two separate inputs rather than one. 7 60 7. Splitting the Brain • Another variation of the Sperry and Gazzaniga’s split brain protocol is shown above. The careful observer might notice that the right hemisphere does not recognize spoon as an image. 61 7. Splitting the Brain • Split brain patient performing the block design test. One can see that the left hand (controlled by the right hemisphere) has less difficulty with this visual analysis task. 62 7. Splitting the Brain • The slide to the left illustrates drawings of the right versus left hands of split brain patients. The drawings completed by the left hand (controlled by the right hemisphere) appear to be less distorted. These findings are not surprising given that the right hemisphere plays a major role in visual-spatial tasks. 63 7. Splitting the Brain • Split brain research supported Broca’s and Wernike’s discoveries that the left hemisphere was a language processor. Even normal split brain subjects show these patterns. That is, when verbal stimuli are presented to the right visual field they are identified faster than if they were presented in the left visual field. The slide to the left illustrates cerebral specialization and function. 64 7. Splitting the Brain • Split and intact brain studies left the scientific community buzzing about cerebral specialization. As a result, educators began to modify learning approaches so they would be consistent with brain research. The cartoon takes a lighter side to the controversy.