Chapter 3 - The Brain PDF

CHAPTER 3: THE BRAIN INTRODUCTION Neuroscience Discovering the structures and processes taking place in the brain Macroscopic view The different parts that make up the brain Microscopic view How neurons compute information THE NERVOUS SYSTEM Nerves and cells throughout the b...

CHAPTER 3: THE BRAIN INTRODUCTION Neuroscience Discovering the structures and processes taking place in the brain Macroscopic view The different parts that make up the brain Microscopic view How neurons compute information THE NERVOUS SYSTEM Nerves and cells throughout the body Receive and transmit information throughout the body 3 goals Gather information Send information to central processor Execute behavior THE NERVOUS SYSTEM: SUBSYSTEMS Central Nervous System (CNS) Brain and spinal cord Peripheral Nervous System (PNS) All other nerves THE NERVOUS SYSTEM: THE CEREBRUM The folded, layered, outer structure of the brain Also known as the cerebral cortex Contains many subcortical regions Encephalization Quotient (EQ) Actual brain size relative to predicted brain size based on body size THE NERVOUS SYSTEM: TERMINOLOGY Dorsal Toward the top Ventral Toward the bottom Caudal/Posterior Toward the back Frontal/Anterior Toward the front THE NERVOUS SYSTEM: TERMINOLOGY Contralateral Signals from one side are processed on the other side Ipsilateral Signals from one side are processed on the same side THE NERVOUS SYSTEM: ASYMMETRICAL PROCESSING Contralateral processing Most information is processed contralaterally Exceptions Trunk and facial muscles Vision processing Left visual field → right hemisphere Right visual field → left hemisphere THE NERVOUS SYSTEM: ASYMMETRY IN THE CORTEX The human brain is asymmetrical Left and right hemispheres Different structures and functions Corpus callosum Thick band of connective tissue between the hemispheres THE CEREBRAL CORTEX: ANATOMY Gray matter (outside) Contains neuron cell bodies White matter (inside) Contains neuronal axons Gyri (gyrus) Sulci (sulcus) ANATOMICAL DIVISIONS OF THE CORTEX Two hemispheres Left hemisphere Right hemisphere Four lobes Frontal lobe Temporal lobe Parietal lobe Occipital lobe FUNCTIONAL LOCALIZATION Functions are localized… Neuropsychology The study of brain function and impairment due to brain pathology Evidence Damage to a specific part of the brain leads to specific impairments FUNCTIONAL LOCALIZATION: HEMISPHERES Left hemisphere: language processing Right hemisphere: spatial processing SPLIT-BRAIN PATIENTS Severed corpus callosum 2 hemispheres can’t communicate During testing, the 2 hemispheres can’t agree on what a person sees! FUNCTIONAL LOCALIZATION: LOBES Frontal lobe Higher level thinking, planning, decision making, movement Parietal lobe Sensation, perception Temporal lobe Hearing, memory Occipital lobe Vision SENSORY & MOTOR CORTICES Motor cortex Involved in the planning of movement Somatosensory cortex Main sensory receptive area for the sense of touch THE CORTICAL HOMUNCULUS THE CORTICAL HOMUNCULUS EVIDENCE OF LOCALIZATION: PHINEAS GAGE EVIDENCE OF LOCALIZATION: APHASIA Broca’s Aphasia Expressive aphasia Slow, deliberate speech Inability to identify and string words together Wernicke’s Aphasia Receptive aphasia Fluid speech that is unintelligible Difficulty understanding language CORTICAL PLASTICITY Reorganization of the brain The brain can change and adapt LIMITATIONS OF COGNITIVE NEUROSCIENCE Tell us something about where and when certain functions are carried out in the brain Depends on the assumption that the brain contains distinct areas that carry out different functions Actually… The brain is an interconnected network Most cognitive functions depend on the distributed activity of many regions working together NEURONS Neurons Nerve cells The basis of cognition Glial cells Auxiliary cells Provide support and protection for neurons NEURONS: ANATOMY NEURONS: ANATOMY Dendrite Branch-like projections Where information (from other neurons) is received Cell Body (Soma) Maintain cell and keep it functional Axon Tube-like structure that carries electrical impulse away from cell body Axon Terminal Output structure of a neuron Passes impulse to another neuron NEURONS: ANATOMY Myelin Sheath Fatty substance to cover the axon Helps axons conduct an electrical signal Node of Ranvier Gaps in the myelin sheath Helps speed transmission Schwann Cell The main glial cells Help form the myelin sheath TYPES OF NEURONS Sensory neurons (Afferent neurons) Input to the nervous system Transduction Association neurons Receive and send information Motor neurons (Efferent neurons) Output of the nervous system NEURONS: CONDUCTING IMPULSES Neurons are electrically charged (negative) Action potential The change in electrical potential associated with the passage of an impulse along the membrane of a neuron All-or-none ACTION POTENTIAL STEPS 1. Resting Potential Neuron is at rest (polarized) 2. Threshold A depolarizing stimulus must be strong enough to reach threshold 3. Depolarization Positive ions rush into the cell, voltage reverses (becomes most positive) 4. Repolarization Positive ions leave the cell 5. Refractory Period The neuron can’t fire again yet (too negative) NEURONS: SYNAPTIC CONNECTIONS Synapse Space between axon terminals and dendrites How neurons communicate with each other NEURONS: SYNAPTIC CONNECTIONS Neurotransmitters Chemical compounds that travel between neurons Lock and key system Neurotransmitters fit into receptors of the receiving neuron NEURONS: SYNAPTIC CONNECTIONS Reuptake Excess neurotransmitters are reabsorbed into the sending neuron Excitatory effect Neurotransmitters cause receiving neuron to fire more quickly Inhibitory effect Neurotransmitters cause receiving neuron to fire more slowly NEUROTRANSMITTERS: LOCK & KEY MECHANISM Agonists Mimic neurotransmitters Excitatory effect Antagonists Block neurotransmitters Inhibitory effect NEUROTRANSMITTERS Acetylcholine Dopamine Glutamate Serotonin Norepinephrine GABA  WITHIN VS. BETWEEN NEURON COMMUNICATION Action Potential Relays a signal within a neuron Electric process Neurotransmitter release How neurons communicate with each other Chemical process NEURAL CIRCUITS Neural circuit A population of neurons interconnected by synapses Carry out a specific function when activated Neural convergence One neuron receives signals from multiple neurons NEURAL CIRCUITS: EXCITATION NEURAL CIRCUITS: EXCITATION NEURAL CIRCUITS: EXCITATION NEURAL CIRCUITS: INHIBITION NEURAL CIRCUITS: INHIBITION NEURAL CIRCUITS: INHIBITION NEURAL CIRCUITS: INHIBITION ENCODING SPECIFICITY Specificity Encoding Hypothesis In higher levels of the brain, a single neuron may be able to code for a very specific object Grandmother Cell hypothesis ENCODING SPECIFICITY Distributed Encoding hypothesis Many neurons are active in response to a single stimulus It’s the pattern of activation that matters EVIDENCE FOR ENCODING SPECIFICITY Monkeys Neurons selectively respond to faces and hands Humans Single cell recordings Conclusive evidence?...probably not ENCODING SPECIFICITY: HYBRID APPROACH Sparse Coding hypothesis A small number of neurons are active for any given complex stimulus The particular combination of neurons is what matters ENCODING SPECIFICITY SUMMARY MEASURING BRAIN ACTIVITY: COGNITIVE NEUROSCIENCE Investigation of neural processes underlying cognition Measuring byproducts of brain activity EEG fMRI TMS ELECTROENCEPHALOGRAPHY (EEG) Measures the electrical activity of the brain through the scalp Event related potential (ERP) Specific changes in electrical charge in response to a presented stimulus FUNCTIONAL MAGNETIC RESONANCE IMAGING (FMRI) Measures the flow of blood in the brain Hemodynamic response The body delivers nutrient-rich blood to active portions of the brain Blood-oxygen-level dependent (BOLD) response What fMRIs actually measure The release of oxygen to active neurons Subtraction method BOLD activity when performing a specific task – BOLD activity when doing nothing/engaging in another task TRANSCRANIAL MAGNETIC STIMULATION (TMS) Can determine the causal effects of specific brain regions on behavior Uses brief, strong magnetic pulses to disrupt electrical activity in the brain Is a specific brain region necessary to carry out a particular task? COGNITIVE NEUROSCIENCE LIMITATIONS Where and when certain functions occur in the brain Not how… ACTION POTENTIAL EXPLANATION SPLIT BRAIN RESEARCH EXAMPLE