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Introducing Neuroscience

Introducing Neuroscience. Aristotle. One of the most influential thinkers in human history However, he thought that the heart and not the brain was the source of sensation, movement, pleasure, etc. Hippocrates.

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Introducing Neuroscience

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  1. Introducing Neuroscience PSY 295 - Fall 2012 - Grinnell College

  2. Aristotle • One of the most influential thinkers in human history • However, he thought that the heart and not the brain was the source of sensation, movement, pleasure, etc... PSY 295 - Fall 2012 - Grinnell College

  3. Hippocrates “Men ought to know that from the brain, and from the brain only, arise our pleasures, joys, laughter and jests, as well as our sorrows, pains, griefs and tears.” [from Kandel 2000] - Hippocrates PSY 295 - Fall 2012 - Grinnell College

  4. Neuroscience • Current views about the brain have emerged in the last 100 years from a variety of research traditions • Scientific investigations of the brain, neurons and behavior collectively comprise the field of Neuroscience PSY 295 - Fall 2012 - Grinnell College

  5. Cell Theory • Zoologist Theodore Schwann proposed that tissues are comprised of cells in 1839 – known as Cell Theory • Initially unclear whether neurons were an exception – many believed that neurons formed a continuous reticulum PSY 295 - Fall 2012 - Grinnell College

  6. Neuron doctrine • Using the Golgi staining method, Spanish neuroanatomistSantiago Ramon y Cajalwas able to label single nerve cells • Cajal advocated the neuron doctrine – individual neurons are the elementary signaling units of the nervous system from Hubel (1995) PSY 295 - Fall 2012 - Grinnell College

  7. Ramon y Cajal PSY 295 - Fall 2012 - Grinnell College

  8. Cajal’s drawings PSY 295 - Fall 2012 - Grinnell College

  9. The Neuron PSY 295 - Fall 2012 - Grinnell College

  10. The Neuron Neurons are cells specialized for transmitting information using fast-traveling electrical impulses called action potentials PSY 295 - Fall 2012 - Grinnell College

  11. Neurons form networks • Neurons form neural networks • Gap between neurons is called a synapse • Synaptic transmission is chemical in nature from Hubel (1995) PSY 295 - Fall 2012 - Grinnell College

  12. How neurons send messages PSY 295 - Fall 2012 - Grinnell College

  13. Resting potential • At rest, due to different concentrations of ions inside and outside the cell, neurons have a polarized membrane potential PSY 295 - Fall 2012 - Grinnell College

  14. Action potential • Chemical signals from other neurons open ion channels, causing neuron to depolarize • When neuron depolarizes sufficiently, voltage-gated channels open, causing a fast, large depolarization called an action potential to propagate down the axon PSY 295 - Fall 2012 - Grinnell College

  15. Action potential PSY 295 - Fall 2012 - Grinnell College

  16. Video PSY 295 - Fall 2012 - Grinnell College

  17. What you need to know • Neurons fire action potentials to sensory stimuli • Signal which permits neuron communication via synapses • Number and/or pattern of action potentials varies with sensory stimulus parameters – neural code PSY 295 - Fall 2012 - Grinnell College

  18. Deep thoughts “As I sit here wondering what it is all about, sodium rushes in and potassium rushes out.” - Cornell bathroom wall (circa 1996) PSY 295 - Fall 2012 - Grinnell College

  19. Sensory systems organization PSY 295 - Fall 2012 - Grinnell College

  20. Cranial nerves PSY 295 - Fall 2012 - Grinnell College

  21. Cranial nerves • Different cranial nerves carry information from different sensory modalities PSY 295 - Fall 2012 - Grinnell College

  22. Cortical specialization • Similarly, different regions of cortex are specialized to represent different sensory modalities PSY 295 - Fall 2012 - Grinnell College

  23. Doctrine of specific nerve energies • Johannes Muller (1801-1858) • States that the nature of a sensation depends on which sensory fibers are stimulated, not how they are stimulated • For instance, if I electrically stimulate your auditory nerve, you will hear sounds PSY 295 - Fall 2012 - Grinnell College

  24. Cochlear implants • In fact, this idea is precisely how cochlear implants work PSY 295 - Fall 2012 - Grinnell College

  25. Idea extends to cortical stimulation • Electrical stimulation of human cortex during neurosurgery causes hallucinatory perceptions (Penfield experiments) • Useful in helping doctor avoid cutting out important brain regions when removing tumors PSY 295 - Fall 2012 - Grinnell College

  26. Methods in Sensory Neuroscience PSY 295 - Fall 2012 - Grinnell College

  27. Neural codes and perception • Single neurons represent sensory stimulus parameters with their rate of action potential firing • Will fire more spikes to some stimuli than others • Relationship between stimulus parameters and neural responses is called the neural code PSY 295 - Fall 2012 - Grinnell College

  28. Studying neural coding Record from single neurons in sensory brain regions while systematically modifying stimulus parameters PSY 295 - Fall 2012 - Grinnell College

  29. Neural codes for visual stimuli V1 – primary visual cortex IT – higher level visual cortex

  30. Tuning curves • A tuning curve relates the response of a neuron to varied stimulus parameters PSY 295 - Fall 2012 - Grinnell College

  31. Thresholds • Just as we can measure sensory thresholds for subjects, we can measure them for neurons PSY 295 - Fall 2012 - Grinnell College

  32. Population code • A working hypothesis accepted by most neuroscientists is that our perceptions are represented by the rates and patterns of action potential firing in populations of sensory neurons • Such a scheme is called population coding http://www.pc.rhul.ac.uk/staff/J.Zanker/PS1061/L6/PS1061_6.htm PSY 295 - Fall 2012 - Grinnell College

  33. Other methods • To study sensory processing in humans, there are a variety of non-invasive methods • These non-invasive methods suffer limitations of not being able to observe action potentials in single neurons PSY 295 - Fall 2012 - Grinnell College

  34. EEG • Electroencephalography or EEG uses scalp electrodes to measure electrical activity from populations of neurons • Average over many trials to get event-related potential (ERP) PSY 295 - Fall 2012 - Grinnell College

  35. Magnetoencephalography (MEG) • Measures changes in magnetic activity arising from electrical activity in large neural populations PSY 295 - Fall 2012 - Grinnell College

  36. MRI • Magnetic Resonance Imaging • Uses responses of atoms to strong magnetic fields to form images of brain structures PSY 295 - Fall 2012 - Grinnell College

  37. fMRI • Measure localized brain activity by measuring localized increases in blood flow • Measures changes of oxygenated and deoxygenated blood to strong magnetic fields (BOLD signal) PSY 295 - Fall 2012 - Grinnell College

  38. PET • Positron Emission Tomography • Another way of measuring regional blood flow using a radioactive substance in bloodstream PSY 295 - Fall 2012 - Grinnell College

  39. Summary • The goal of sensory neuroscience is to explain our perceptions in terms of the activities of neurons • A wide variety of techniques are used to study brain events which may represent perceptual events • Techniques are always improving PSY 295 - Fall 2012 - Grinnell College

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