Lecture 7Three big questions:1) How does the world get inside our heads? How is it represented in the brain?- The outside world must be coded somehow and represented that way in the brain2) Neuronal plasticity: experience somehow modifies the brain; these modifications can persist over time and change the probability of behaviors (learning, memory)3) Neural basis of motivation, reinforcement, emotion: what brain events and processes underlie reward and reinforcement? How do these get linked up with the learning systems?Reductionism: the attempt to explain complex phenomena by reducing them to simpler and already understood componentsEx: CA+ channels opening when poking a snail, understood more simply as habituation and forgetting the habituation when you later poke it and its gills withdraw againThe brain wasn’t designed- it evolved; designed by natural selectionMaclean: mammalian triune brain  accumulative development of the brain. Model of the evolution of the vertebrate forebrain and behaviorTripling of brain volume over 4 million years implies that within a species there were heritable individual differences in brain sizeSelection pressures: plans for action; the brain is a tool for anticipating and thinking things out, represents the world; the brain lets us tote the world around inside our heads and operate on it; gives us control of the environment- Complex mental and behavioral events are ultimately based on neuronal activity a very large number of simple units (neurons) that fire or don’t fire, and have excitatory or inhibitory influences on other unitsNeuron: dendrites, axon, nucleus, myelin sheathNeuron’s rate of firing is important for neural coding- representing the info in the stimulus- Antipsychotic drugs alter the rate of fire of the neuron- Neurotransmitters: chemical communication across the synapse; influence the probability of firing the post-synaptic neuronSensitization: strong USC (shock)  increased responsiveness to any new stimulus (opposite of habituation); three kinds of neuron are involved1) Habituate to siphon touch2) Shock to tail3) Retest siphon touchBlack triangle: connection has become inhibitoryLesioning experiments: train a conditioned response. Does the CR still exist after cells are destroyed (lesioned) in a given brain area?Lesioning abolishes the CR, can never be re-learnedUCR still intact- importantEx: rabbit was trained to blink (CR), after lesioning he will blink when there is wind in his eye (UCR still in tact)- Long-Term Potentiation (LTP): done with small groups of neurons; repeated A:C activations lead to structural changes and function of the synapse to make it faster and more automatic; change in the brain induced by experienceArtificial electrical activation of neurons puts them into a potentiated state: can be activated by later weak stimulation which was ineffective prior to LTP- Gene augmentation: give them extra copies of an alleleDisplays more LTP; learns associations faster; more post-synaptic receptors- Neuronal plasticity: brain changes as a result of experienceEx: blind people don’t use their occipital lobe, and so the brain uses this for other functionsMusical practice (instrument, voice) results in changes to the brainLecture 8Brain Imaging Methods:PET (position emission tomography): neural activity inferred from detection of radiation products.Highly invasive (radioactive decay products)MRI (magnetic resonance imaging): Create a picture of brain structures by “reflection” of RF signals. Uses high-strength magnetic fields to align molecules.Detecting regional cerebral blood flowfMRI measure brain activity as well as structure.Determine what parts of the brain detect specific stimulationfMRI shows the difference between the activation of the brain when looking at a reference stimulus and the activation when looking at the specific stimulation being measuredLarge differences appear as hot colorsNeed a control task to compare it to the experimental taskSubtraction Method: Suppose you want to know what brain areas (if any) respond specifically to visual stimulation produced by objects in motionCompare activations produced by a static visual stimulus (a grid) with activations produced by a moving object.Show the difference between them (object activations minus grid activations) as fMRI images, with large differences appearing as “hotter” colors.MEG (magnetoencephalography): Detects weak magnetic fields produced by neural activity.EEG (electronencephalography): Measure electrical activity (voltage changes) over cortical surfaces (“evoked potentials”).High temporal resolution, low spatial resolution (limited to cortical surface activity)Sensing electrodes respond to voltage changes over cortical surfaces produced by the electrical activity of the brain. These are then amplified and displayed.rTMS Repetitive Transcranial Magnetic Stimulation: temporary disruption of electrical activity of the brain.Effects the ongoing activity of neurons in the cortexCan shut down activity in part of the brain and reverse it back to normalrTMS can interfere with the function of mirror neurons that are important in learning by imitation; can also be used to selectively disrupt memory store and retrievalSingle-unit recording: Measure activity of small sets of neurons or individual neurons.Not for the use of punishmentStudying sensory coding in the brain- These methods of observing brain activity differ in invasiveness, temporal resolution, and spatial resolution (and cost)g = general intelligenceDifferences in where the brain lights up between people with higher test scores and lower test scoresTracing mental activity with sensing electrodes:Retina  LGN  V1 (simple visual forms, edges, corners)  V2  V4 (intermediate visual forms, feature groups)  PIT  AIT (recognition, meaning, associations)  PFC (categorical judgments, decision making)  PMC  MC (motor command)  to spinal cord  to finger muscleHappens in a quarter of a secondV2, V4 = visual analysisParts of the brain in accordance:•RETINA (regarded as being part of the brain)• LGN: LATERAL GENICULATE NUCLEUS OF THALAMUS•OCCIPITAL LOBES V1-V4 AREAS• TEMPORAL LOBE: POSTERIOR INFERIOR, ANTERIOR INFERIOR• PFC: PREFRONTAL CORTEX• PMC PREMOTOR CORTEX• MOTOR CORTEX• EFFECTORS- Endophenotype: fundamental brain-based response, observable behaviorMotivation: The Basics (new PowerPoint)What are the reasons for a