Homework 1

This problem set is due Tuesday (9/7/2021) at 11:58 pm. Please turn in your work by uploading to Canvas. If you have questions, please post them on the course forum, rather than emailing the course staff. This will allow other students with the same question to see the response and any ensuing discussion. The first goal of this problem set is to review the concept that complex operations involve distributed action in the brain and to think about how best we can understand the process of cortical computaiton. The second goal is to review molecular neurobiology.

  1. Organization of the brain - short answer (a few sentences, 5 pts) In the 1860s, Pierre Paul Broca described how patients with lesions in the posterior left frontal lobe (what is now called “Broca’s area”) were capable of understanding language but not speaking.

    How do the symptoms of lesions in Wernicke’s area differ from those in Broca’s area?

    What happens to deaf patients ability to communicate in sign language when they suffer damage to Broca’s or Wernicke’s areas?

  2. The Stroop Effect (5 pts) Please take the Stroop effect test at http://www.math.unt.edu/~tam/SelfTests/StroopEffects.html. What was your performance time for the congruent and incongruent samples? What factors do you think might affect your performance? How do you think you could improve? For full credit, record your answer on the Canvas HW1-Stroop Effect Survey.

  3. The MindScope Projet (10 pts) Read this recent paper describing the Allen Institute’s MindScope Project: “Inferring cortical function in the mouse visual system through large-scale systems neuroscience” Hawrylycz et al PNAS 2016 (PDF).

    In the mammal, what “big picture” three regions of neurons process visual input? Which is the most complex? How many different kinds of neurons are there in mouse visual cortex?

    The “overarching goal of Mindscope is to understand the operations and the flexibility of cortical tissue in the mouse by comprehensively recording and analyzing cellular-level cortical responses.” At what levels is this project investigating the mouse visual nervous system? At which of these levels do you think they have the best chance of achieving their goal?

  4. Distributed Functions (10 pts) Watch the Neuralink “Progress Update” https://www.youtube.com/watch?v=DVvmgjBL74w. What examples of applications of their technology would be made challenging by the distributed aspects of some mental processes?

  5. Similarity of Function Across Species (10 pts) The Nobel Prize in 2014 was awarded for the discovery of two different patterns of neural responses in memory-related regions of the brain. Here is an overview: https://www.sciencedirect.com/science/article/pii/S0896627314010903 Recently, a similar pattern was observed in the brains of birds http://science.sciencemag.org/content/373/6552/343.long.

    What is the name given to the receptive fields of this type of neural activity? This activity was not observed in all types of birds. Why do the authors speculate this is?

  6. Attention and Top-Down vs Bottom-Up (10 pts) View the double drift illusion here: https://www.sciencedirect.com/science/article/pii/S0960982219313739 Why do you think your perception of the drift differs when you look at the fixation point versus looking at the drift stimulus?

  7. Neurons and Glia (10 pts)

    Our estimates of the numbers of neurons and glia in the brain have changed over time. (If your curious about the history of this, see Bartheld et al, J Comp Neuro 2016. Glia now seem potentially less important than they once did. This paper (Sherwood et al, PNAS 2006 suggests one reason why there are more glia per neuron in humans than other primates. What is it?

  8. Membrane Potentials and the Nernst Equation (40 pts)

    Refer to PNS Chapter 7 for an explanation of the Nernst and Goldman equations. As discussed in class, a neuron’s resting potential is determined by the relative intra- and extra-cellular ion concentrations and the corresponding conductivities of the respective ion channels. For a permeable membrane, if an equilibrium is established (i.e., by active transport) in which the concentration of an ion is different on either side but net passive flow of ions in and out is zero, an electric potential (a voltage) will exist which represents the point at which the force of diffusion is balanced by electrostatic forces. The Nernst equation gives the voltage as a function of the inside and outside concentrations.

    a. Use the Nernst equation to fill in the equilibrium potentials for potassium, sodium, and chloride in the table below. (10 pts)

    Ion Extracellular Concentration Intracellular Concentration Permeability Equilibrium Potential
    K+ 20 mM 400 mM 1  
    Na+ 440 mM 50 mM 0.04  
    Cl- 560 mM 52 mM 0.45  

    When the membrane is permeable to multiple ions, the equilibrium that is established is similar, with the relative permeability for each ion determining its impact on the final membrane potential in addition to its external and internal concentrations. The Goldmann equation (or GHK) gives the equilbrium potential as a function of concentrations and relative permeabilities.

    b. Taking into account the potassium, sodium, and chloride concentrations, calculate the resting potential of a neuron with the characteristics in the table above. (10 pts)

    c. How could you adjust the potassium level to raise the resting potential? Why does this work? (10 pts)

    d. Calculate the new extracellular potassium concentration that would be needed to bring the resting membrane potential to -65mV. To counteract the decrease in potassium concentration, the cell could insert or remove ion channels into the membrane thus changing the permeability ratio. How might the cell recover the original resting membrane potential and calculate the new permeability ratio? (10 pts)

  9. Synapses (10 pts)

    Refer to PNS Ch. 10 and Ch. 12 and the Lecture 3 slides.

    a. Synapses can be either ionotropic or metabotropic. What is the difference between these two categories? Which are faster?

    b. What are the main excitatory and inhibitory neurotransmitters?

    c. Rods and cones are the two main photoreceptors in the retina. They project to bipolar cells, who project to retinal ganglion cells which then transmit information down the optic nerve to the brain. This paper is a good reference - Masland, Nature Neuroscience 2001 What kind of synapses do cones make onto bipolar cells? How do you think this affects vision.