Unit 3 - Biological Bases of Behavior

1. Unit 3 - Biological Bases of Behavior

2. Why study biology in a psychology class? • “Everything psychological is simultaneously biological.” • Every thought, behavior, emotion, perception, etc. is rooted in our biology, particularly our brain • The brain is a “psychological organ” as well as a biological one • Biological psychology: studies the link between our biology and our behaviors and mental processes • a.k.a. biopsychology, neuroscience

3. Starting small: The Neuron • neuron: a nerve cell; receives signals from other neurons or sensory organs, processes these signals, and sends signals to other neurons, muscles, or bodily organs • the basic unit of the nervous system

4. The Neuron • 3 types of neurons: • 1. sensory neurons: respond to input from sensory organs (skin, eyes, etc.) • 2. motor neurons: send signals to muscles to control movement • 3. interneurons: connect the sensory neurons and motor neurons • most of the neurons in the brain = interneurons • average human brain  100 billion neurons • plus 10x as many glial cells • glial cell: a cell that fills the gaps between neurons, facilitate communication between neurons, and help in the care and upkeep of neurons

5. Structure of the Neuron

6. Structure of the Neuron • cell body (soma): the central part of the neuron, contains the nucleus • regulates cell functioning • dendrites: the branching part of the neuron that receives messages from other neurons and relays them to the cell body

7. Structure of the Neuron • axon: the long, cable-like extension that delivers messages to other neurons • myelin sheath: layer of fatty tissue that insulates the axon and helps speed up message transmission • multiple sclerosis: deterioration of myelin leads to slowed communication with muscles and impaired sensation in limbs • terminal button: structure at the end of one of the axon’s branches that releases chemicals into the space between neurons, when the neuron is fired

8. The Neuron in Action • resting potential: the negative charge maintained within neurons that are at rest • due to more sodium ions outside neuron than inside, and more potassium inside neuron than outside • messages from other neurons are either excitatory (like pushing the neuron’s accelerator) or inhibitory (like pushing the neuron’s brakes) • threshold: the level of stimulation required to trigger a neural impulse

9. The Neuron in Action • When the threshold is reached, channels in the cell membrane open and allow transfer of sodium and potassium ions • action potential: a neural impulse; the shifting change in charge that moves down the axon to terminal buttons • all-or-none law

10. From Neuron to Neuron • ≈100 billion neurons in a human brain, connected to an average of 10,000 others; some up to 100,000 (Shepherd, 1999) • synapse: the place where an axon of one neuron meets with the dendrite/cell body of another neuron

11. From Neuron to Neuron

12. From Neuron to Neuron • synaptic cleft: the gap between the axon and the dendrite/cell body across which neural transmission occurs • neurotransmitters: a chemical that sends signals from one neuron to another over the synaptic cleft

13. From Neuron to Neuron • Neurotransmitters are stored in vescicles in the terminal buttons, and bind to receptors on the cell membrane of the next neuron. • Each receptor can only bind with one kind of neurotransmitter. • Some of the neurotransmitter remains in the synaptic cleft, needs a special chemical reaction to reuptake (reabsorb) to vescicles

14. Neurotransmitters at Work:An Example • Low levels of the neurotransmitter serotonin have been associated with clinical depression. • depression treated with selective serotonin-reuptake inhibitors (SSRIs) • e.g. Prozac, Zoloft, Paxil

15. (Some) Neurotransmitters

16. The Nervous System • comprised of the central nervous system and the peripheral nervous system • central nervous system: brain and spinal cord • 31 pairs of spinal nerves radiate from the spinal cord • reflex: an automatic response to an event • e.g. sensory neuron detects pain, send signal to spinal cord  signal to interneurons  signal to motor neurons • Why the middle man of interneurons? To allow brain to prevent reflex responses when appropriate

17. The Nervous System • Peripheral Nervous System: links central nervous system to organs • comprised of the skeletal nervous system and the autonomic nervous system • skeletal nervous system: controls voluntary movements of our skeletal muscles

18. The Nervous System • autonomic nervous system: controls many of the self-regulatory functions of the body (e.g. digestion, circulation) • comprised of the sympathetic and parasympathetic nervous systems • sympathetic: prepares us for defensive actions against threats (e.g. faster heartrate, increased breathing rate, inhibits digestion, dilates pupils to allow greater light sensitivity) • parasympathetic: counteracts effects of sympathetic nervous system, calms us down

19. Structure of the Brain • The human brain is comprised of “older” and “newer” parts. • “older”: lower level structures, responsible for basic survival mechanisms • “newer”: higher level structures, responsible for more advanced human faculties

20. Structure of the Brain • brainstem: the set of neural structures at the base of the brain, including the medulla, the reticular formation, and the pons • facilitates communication between the brain and spinal cord

21. The Brainstem • medulla: controls heartbeat, breathing, and swallowing • reticular formation: regulates alertness and autonomic nervous system activity • pons: bridge from brainstem to cerebellum; controls a variety of functions, including sleep and control of facial muscles

22. The Cerebellum • “little brain” extending from rear of brainstem • coordinates physical movement • contributes to estimating time and paying attention • cerebellum + other lower level brain structures occur without conscious effort • Much of our brain’s activity occurs outside of our awareness

23. The Brainstem • thalamus: the brain’s sensory switchboard; receives signals from the sensory and motor systems, and relays them to the appropriate parts of the brain • also receives signals from higher brain structures, relays them to medulla and cerebellum

24. The Limbic System • limbic system: doughnut-shaped system of neural structures at the border of the brainstem and cerebral hemispheres • involved in the basics of emotion and motivation: fighting, fleeing, feeding, and sex • comprised primarily of the hypothalamus, the hippocampus, and the amygdala

25. The Limbic System • hypothalamus: brain structure that sits under the thalamus and plays a central role in controlling eating and drinking, and in regulating the body’s temperature, blood pressure, and heart rate • “pleasure center”? (Olds & Milner, 1954)

26. The Limbic System • hippocampus: brain structure that plays a key role in allowing new information to be stored in memory • patient H.M. • hippocampus does not contain memories itself, but does trigger processes that store memories elsewhere in the brain

27. The Limbic System • amygdala: almond-shaped structure that plays a critical role in anger and fear • Lesioning the amygdala of the rhesus monkey turns the animal into a mellow, “unangerable” creature (Kluver & Bucy, 1939). • Electrically stimulating one part of the amygdala leads to anger response in cats; another spot leads to fear response.

28. The Visible Brain • cerebral cortex: the convoluted pinkish-gray surface of the brain, where most mental processes take place • The brain is divided into two halves (cerebral hemispheres), separated by a deep fissure • hemispheres control opposite side of body (e.g. right-handers’ writing is controlled by the left hemisphere)

29. Our Divided Brains • cerebral hemispheres connected by the corpus callosum, a large band of neural fibers that transmits messages between hemispheres • contains more than 200 million nerve fibers, can transfer more than 1 billion bits of information per second

30. Our Divided Brains • evidence of hemispheric specialization? • left brain: written language, spoken language, number skills, reasoning (analytical and verbal) • right brain: insight, art awareness, imagination/creativity, music awareness (intuitive and perceptual) • But it’s not as simple as simply “left-brained” and “right-brained”... The two hemispheres continually work together on most tasks.

31. Our Divided Brains • How do we know about hemispheric specialization? • split-brain patients: people whose corpus callosum has been severed for medical purposes, so that neuronal impulses no longer pass from one hemisphere to the other • used to treat epilepsy: a disease that results in massive amounts of uncontrolled neuronal firing that leads to seizures • prevents spasm from engaging both hemispheres, thus limiting its severity • split-brain patients typically function well; personality and intelligence intact

32. Split Brains • left half of both eyes’ field of vision sent to the right hemisphere; right half sent to left hemisphere • corpus callosum allows hemispheres to share information • in split brains, information is confined to the hemisphere that receives it • Objects in the left half of the visual field can be difficult or impossible to see and name. But they are still seen...

33. The Visible Brain • The brain has “wrinkles” to increase surface area, while keeping the brain compact. • sulcus (plural = sulci): a crease in the brain • gyrus (plural = gyri): a bulge between sulci in the cerebral cortex • cerebral cortex alone contains roughly 30 billion neurons and 300 trillion synaptic connections

35. Structure of the Cortex • cerebral cortex divided into lobes, or regions of the brain • Each lobe is (roughly) responsible for different higher-level functions, but remember that they do not work merely in isolation.

36. Structure of the Cortex • occipital lobe: brain lobe at the back of the head • responsible primarily for vision; separate areas specify visual properties such as shape, color, and motion

37. Structure of the Cortex • temporal lobe: the brain lobe under the temples, in front of the ears • many functions, including processing sounds, committing information to memory, and comprehending language

38. Structure of the Cortex • parietal lobe: brain lobe at the top and center/rear of the head • involved in registering spatial location, attention, and motor control • also involved in arithmetic • Einstein’s parietal lobes were found to be about 15% bigger than average (Witelson et al.,1999)

39. Structure of the Cortex • sensory cortex (a.k.a. somatosensory strip): the gyrus immediately behind the central sulcus • registers sensation on the body, and is organized by body part

40. Structure of the Cortex • sensory cortex (a.k.a. somatosensory strip): the gyrus immediately behind the central sulcus • registers sensation on the body, and is organized by body part

41. Structure of the Cortex • frontal lobe: the brain lobe located behind the forehead • the seat of planning, memory search, motor control, reasoning, emotions, and many other functions • In many ways, the frontal lobe is what makes us uniquely human.

42. Structure of the Cortex • motor cortex: the gyrus immediately in front of the central sulcus • controls fine movements and is organized by body part (just like the sensory cortex)

43. Mapping Brain Functions • How do we know that different lobes of the brain are responsible for distinct functions? • brain damage patients • e.g. Phineas Gage • marked personality differences, and trouble with social interactions after frontal lobe damage • e.g. stroke victims

44. Mapping Brain Functions • electroencephalograph (EEG): an amplified recording of the pulses of electrical activity (“brainwaves”) that sweep across the brain’s surface • advantages: • tracks electrical activity either in response to a specific stimulus or over time (high temporal resolution; 1 msec) • non-invasive • drawback: electrodes on scalp do not demonstrate precise location of the electrical current

45. An Electroencephalogram

46. Neuroimaging Techniques • brain scanning techniques that produce a picture of the structure or functioning of neurons • computer-assisted tomography (CT scan): the oldest neuroimaging technique (1971 prototype), produces a 3D image of brain structure using X-rays • advantages: • allows direct view of level of interest • high-contrast resolution • disadvantage: potential for damage due to high levels of radiation

47. Neuroimaging Techniques • positron emission tomography (PET scan): a neuroimaging technique that uses small amounts of radioactive glucose to track energy consumption in the brain (functionality) • neurons use more glucose when active; radioactive injection delivered to most active areas of brain • as the radioactive isotope decays, it shoots off protons, which then give off a small burst of light when they meet with the scanner • advantage: provides an estimate of amount of glucose consumption in each part of the brain • drawbacks: • radiation exposure • lengthy process (up to 40 seconds of brain activity to build an image) • expensive equipment necessary to create radioactive isotopes

48. PET Scans Dementia patient’s brain Normal human brain

49. Neuroimaging Techniques • magnetic resonance imaging (MRI): a technique that uses magnetic properties of atoms to take sharp pictures of the structure of the brain (and other soft tissue) • different atoms resonate to different frequencies of magnetic fields • background magnetic field aligns all the atoms in the brain • second magnetic field turned on/off repeatedly many times per second • atoms align with second field at proper frequency, then swing back to background when second field is turned off

50. Neuroimaging Techniques • functionalmagnetic resonance imaging (fMRI): a type of MRI that detects the amount of bloodflow in different regions of the brain • bloodflow = proxy for oxygen delivery • MRI = structure, fMRI = function • advantages: • indicates specific regions of activity (high spatial resolution, 3-6 millimeters) • non-invasive, does not require radiation or X-rays • quick process (only a few seconds) • disadvantages: • brain is never “off”, consistently consuming oxygen • fMRI compares brain function while doing a task vs. at rest (but what’s going on in rest?) • can be uncomfortable for participant (lie very still in a small, noisy tube)