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Chapter 4

Chapter 4

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University of Toronto St. George
Dan Dolderman

Chapter 4 – The Brain and Consciousness phrenology – the practice of assessing personality traits and mental ability by measuring bumps on the human skull. (not valid scientifically however) equipotentiality – idea that all parts of the cortex contributed equally to mental ability. What are the Basic Brain Structures and their Functions? The Spinal Cord is capable of autonomous (Independent) Functions spinal cord – part of the CNS, a rope or neural tissue that runs inside the hollows of the vertebrae from just above the pelvis and into the base of the skull. gray matter - a segment of the spinal cord that is dominated by the cell bodies of neurons. white matter – a segment of the spinal cord consisting mostly of axons and the fatty sheaths surround them. stretch reflex – the conversion of sensation into action by a handful of neurons and the connections between them. The Brainstem Houses the Basic Programs of Survival Brainstem – a section of the bottom of the brain that houses the most basic programs of survival, such as breathing, swallowing, vomiting, urination and orgasm. The brainstem uses the reflexes of the spinal cord to produce useful behaviours. Reticular formation- a large network of neural tissue within the brainstem involved in behavioural arousal and sleep-wake cycles. The Cerebellum is Essential for Movement Cerebellum – a large convoluted protuberance at the back of the brainstem that is essential for coordinated movement and balance. The most obvious role of the cerebellum is in motor learning. Patients with disorders of the cerebellum typically have symptoms of ataxia, which involves clumsiness and a loss of motor function. Subcortical Structures Control Basic Drives and Emotions (figure pg. 124) Above the brainstem and cerebellum is the forebrain, which consists of the two cerebral hemispheres. The most noticeable feature of the forebrain is the cerebral cortex. Below this are the subcortical regions (hypothalamus, thalamus, hippocampus, amygdale, and basal ganglia. Hypothalamus – a small brain structure that is vital for temperature regulation, emotion, sexual behaviours and motivation. The hypothalamus receives input from almost everywhere and projects its influence to almost everywhere. It controls the pituitary gland (master gland of the body) through releasing hormones. Thalamus – the gateway to the brain that receives almost all incoming sensory information before it reaches the cortex (except for the sense of smell which has a direct route to the cortex). Hippocampus & Amygdala Hippocampus – role in storage of new memories. It does this by creating new interconnections within the cerebral cortex. It can increase in size with increased usage (taxi drivers in London). Amygdala – serves a vital role in our learning to associate things with emotional responses and for processing emotional information (e.g. a disgust response upon unpleasant food). The amygdala also plays a role in responding to stimulus that elicit fear. The Basal Ganglia Basal ganglia – important for the initiation of planned movement. The nucleus accumbens is one structure within the basal ganglia. Everything that you do that is pleasurable is associated with activation of dopamine neurons in the nucleus accumbens. The Cerbral Cortex Underlies Complex Mental Activity (figure pg. 125) Cerebral cortex – the outer layer of the brain tissue that forms the convoluted surface of the brain The cerebral cortex is the site of all thoughts, detailed perceptions and consciousness. Each hemisphere has four lobes: the occipital, parietal, temporal and frontal. A bridge called the corpus callosum connects the two hemispheres and allows information to flow between them. Occipital lobes – region of the cerebral cortex at the back of the brain that is important to vision. Left side of hemisphere takes information from the right side of the visual field and vice versa. (Image on right side – right eye – left hemisphere). Parietal lobes - a region of the cerebral cortex in front of the occipital lobes and behind the frontal lobes that is important for the sense of touch and the spatial layout of the environment. Temporal lobes – the lower region of the cerebral cortex that is important for processing auditory information and also for memory. Frontal lobes – the region at the front of the cerebral cortex concerned with planning and movement. Prefrontal cortex – region of the frontal lobes, important for attention, working memory, decision making, appropriate social behaviour and personality. Frontal lobe (thought, planning movement) Parietal Lobe (touch, spatial relations) Occipital Lobe (vision) Temporal Lobe (hearing, memory) How does the Brain Change? Plasticity – a property of the brain that allows it to change as a result of experience, drugs or injury. The Interplay of Genes and the Environment Wires the Brain The environment does not just affect the product’s of our DNA’s activity, it affect the DNA’s activity itself. Chemical Signals Guide Growing Connections Neuron/ axon growth are inspired by chemical gradients (growth towards or away from etc.) Experience Fine Tunes Neural Connections Critical period – the time in which certain experiences must occur for normal brain development, such as exposure to visual information during infancy for normal development of the brain’s visual pathways. The Brain Rewires itself Throughout Life Hebbian Learning – if two neurons fire at the same time, it strengthens the connection between them. Another possible method of plasticity if the growth of entirely new connections. Neurogenesis – new neurons produced in an adult brain. There appears to be a fair amount of neurogenesis in the hippocampus. Recall that memories are retained within (or require) the hippocampus before being transferred to the cortex. Changes in use distort cortical maps. All the maps in the cerebral cortex shift in response to their activity. The Brain can Recover from Injury Following a lesion in the cortex, the surrounding gray matter assumes the fuction of the damaged area, which the map distorting everywhere around it to recover the lost capability. Such plasticity involves all levels of the nervous system, from the cortex down to the spinal cord. How is the Brain Divided? The Hemispheres Can Be Separated Corpus callosum – a fibre of axons that transmits information between the two cerebral hemispheres of the brain. Split brain – a condition in which the corpus callosum is surgically cut (usually to localize seizure activity to one side of the brain) and the two hemispheres of the brain do not receive information directly from each other. Using the split-brain experiment (see psy100 lecture 4 notes), it has been shown that splitting the brain, produces two half brains, each with its own independent perceptions, thoughts, and consciousness! The Hemispheres are Specialized Left hemisphere – has more speech and recognition Right hemisphere – has more spatial relatio
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