1) Drop off in the Bi 150 box outside Baxter 331 or to the head TA (jcolas).

Transcription

1 Bi/CNS/NB 150 Problem Set 5 Due: Tuesday, Nov. 24, at 4:30 pm Instructions: 1) Drop off in the Bi 150 box outside Baxter 331 or to the head TA (jcolas). 2) Submit with this cover page. 3) Use a separate sheet of paper for each problem. 4) Type all answers if possible. 5) Use complete, grammatically correct sentences. 6) Include your name and the page number on every page. 7) Note that late problem sets receive a 10% deduction for every day past the due date. Name: Time and date submitted: Total pages (including cover page): Comments: Problem 1 grade: Problem 1 comments: Problem 2 grade: Problem 2 comments: Total grade: 1

2 Problem 1 (1.5 points): Sensorimotor systems Problem 1.A (0.4 points): Sense of self 1.A.a. Even with your eyes closed, you generally still know where your arms and legs are located. How can you know the position of your body without looking? Name the sensory modality used for this and briefly describe the peripheral mechanism for sensing it. Proprioception (including kinesthesia). Among other mechanisms, the muscle spindle and the Golgi tendon organ contribute to this sense. (0.1 pt) 1.A.b. Describe the most relevant pathway that mediates this sensory modality. Include every step as you trace the pathway from the periphery to cerebral cortex. Provide the specific names of the structures involved at each stage of processing. Also state if any connection crosses to the other side of the body or brain. Alternatively, you can draw a detailed diagram of the pathway and clearly label the stages of processing. Dorsal-column-medial-lemniscus pathway. In the periphery first-order neurons have somas in the dorsal-root ganglia and receptors in joints and muscles. These neurons project to the central nervous system with axons ascending in the ipsilateral dorsal column of the spinal cord. The first-order neurons synapse onto second-order neurons in dorsal-column nuclei, the gracile nucleus and cuneate nucleus. These second-order neurons in turn project axons up the medial lemniscus, which decussates (crosses) to the other side of the brainstem and projects to the ventral posterolateral nucleus of the thalamus. This in turn projects to primary somatosensory cortex. (0.3 pt) (Names of dorsal-column nuclei not necessary for full credit.) Problem 1.B (0.3 points): Two-point discrimination 1.B.a. A test of two-point discrimination examines one s ability to discriminate touching at two different points from touching at one point. Which part of the body would be most sensitive for such discrimination? Justify your answer. Finger tips or face due to disproportionate representation. (0.1 pt) 1.B.b. How can this fine sensitivity be achieved? Describe at least two distinct properties that contribute to better two-point discrimination. 1) Greater density of sensory receptors at a particular location 2) Greater numbers of dedicated neurons at all stages of processing, including cerebral cortex (e.g., cortical homunculus) 3) Lateral inhibition at the network level, such as in dorsal-column nuclei (0.2 pt) 2

3 Problem 1.C (0.4 points): Pathways 1.C.a. A doctor is examining a patient with a complete lesion of one half of the spinal cord only at the L1 level. The patient has paralysis in the left leg. Which pathway on which side of the spinal cord is damaged? The left corticospinal tract at the L1 level is damaged. (0.1 pt) 1.C.b. Next, the doctor checked whether the patient could feel pain at each part of the body. Does the patient have difficulty sensing pain? If so, state which part of the body has the defect and describe the relevant pathway. Yes, the right leg has the defect because of damage to the left anterolateral pathway (or spinothalamic tract) at the L1 level. (0.15 pt) 1.C.c. Finally, the doctor checked whether the patient could feel touching with a fine hairbrush at each part of the body. Does the patient have difficulty sensing touch? If so, state which part of the body has the defect and describe the relevant pathway. Yes, the left leg has the defect because of damage to the left dorsal-column-mediallemniscus pathway at the L1 level. However, some limited information could be transmitted via the anterolateral pathway (or spinothalamic tract). This anterolateral representation would be much less precise, so the patient would still have some difficulty discriminating when and where the brush touches. (0.15 pt) Problem 1.D (0.4 points): Comparisons across systems Rank the sensory systems underlying vision, audition, olfaction, and somatosensation in order from least to most with respect to each of the following criteria. Explain the reasoning behind the rankings. 1.D.a. Temporal acuity (i.e., how precisely in time the system can detect stimuli) Olfactory < Visual < Somatosensory < Auditory This order reflects each system s capacity to discriminate repeated stimuli. The order may differ slightly depending on the definition of temporal acuity used. (0.05 pt for each ranking and 0.05 for each explanation) 3

4 1.D.b. Spatial acuity (i.e., how precisely in space the system can detect stimuli) Olfactory < Auditory < Somatosensory < Visual Olfactory < Somatosensory < Auditory < Visual This order reflects each system s capacity to discriminate spatially separated stimuli. Comparisons of the minimum detectable angular diameter are straightforward for the olfactory, auditory, and visual systems. The order may differ slightly depending on the definition of spatial acuity used. 1.D.c. Relative importance to humans (i.e., the degree of impairment to everyday life that would result from loss of the system) Olfactory < Somatosensory < Auditory < Visual Olfactory < Auditory < Somatosensory < Visual Olfactory < Somatosensory < Visual < Auditory Some other rankings could also be valid because the order largely depends on the individual s priorities. For example, research has shown that musicians would be more likely to choose blindness over deafness. 1.D.d. Amount of primary sensory neocortex devoted to the system in humans Olfactory < Auditory < Somatosensory < Visual The olfactory system includes allocortex (3, 4, or 5 layers) rather than neocortex (6 layers). 4

5 Problem 2 (1.5 points): Learning & Memory Problem 2.A (1.0 points): Taxonomy 2.A.a. Define episodic memory and semantic memory. Episodic memory is memory for events and personal experience. Semantic memory is memory for facts. (0.1 pt) 2.A.b. Provide an example of each of these two types of memory and explain what about the examples determines their inclusion in either category. There are many examples that are easy to find. (0.75 pt) 2.A.c. Which broader category of memory do these two types fall under? Both are types of explicit memory. (0.75 pt) 2.A.d. Where specifically would a brain lesion most selectively impair episodic memory? Lesions in hippocampus or association areas of the frontal lobes would selectively impair episodic memory. (0.75 pt) 2.A.e. Where specifically would a brain lesion most selectively impair semantic memory? Semantic memory is stored in distributed networks. Lesions in several of these distributed regions throughout neocortex and especially temporal cortex would selectively impair semantic memory. (0.75 pt) 2.A.f. Define associative learning and non-associative learning With associative learning the animal learns about the relationship between two stimuli or between a stimulus and a behavior. With non-associative learning the animal learns about the properties of a single stimulus. (0.1 pt) 2.A.g. Categorize each the following types of learning as either associative or nonassociative: sensitization, habituation, classical conditioning, and operant conditioning. Sensitization and habituation and non-associative, whereas classical conditioning and operant conditioning are associative. (0.1 pt) 5

6 2.A.h. Define each of the aforementioned four types of learning and provide examples of how each would be demonstrated in an experiment. Emphasize what is unique about each type. Describe what you would do and what you would measure in the experiment. Habituation entails a reduced response to repeated stimuli, such as a reduced startle response to repetitive sound stimuli. Sensitization is essentially the opposite of habituation and entails an enhanced response. Classic conditioning is the association of an unconditioned stimulus and a conditioned stimulus, such as in Pavlov s dog experiments. Operant conditioning is the association of a particular behavior and an outcome stimulus, such as with an animal learning to push a lever for food. (0.3 pt) 2.A.i. What is the most obvious difference in recollection between the two major types of memory described in 2.A.a. and 2.A.g.? Recollection of explicit/declarative memory (2.A.a.) involves conscious experience of the memory itself, whereas recollection of implicit/nondeclarative memory (2.A.g.) is unconscious and unintentional. (0.1 pt) Problem 2.B (0.5 points): Temporal aspects 2.B.a. Name and briefly describe at least four distinct stages in time at which learning and memory operate. 1) Encoding is the learning of new information. 2) Consolidation is the stabilization of a memory trace so that the newly formed information perseverates. 3) Storage is the retaining of memory over time. 4) Retrieval is the recollection of stored information. 5) Reconsolidation is another stage of consolidation of memories upon recollection. (0.2 pt) (Reconsolidation not necessary for full credit.) 6

7 2.B.b. What are the differences among iconic memory, short-term memory, working memory, and long-term memory? Include the time scales over which each of these different forms of memory are active and the region(s) of the nervous system responsible for them in humans. Iconic memory (< 1 s) is short-term sensory memory stored in the regions dedicated to the sensory modality. Short-term memory (< 30 s) is limited to a small amount of information and a short period of time but is in an active and readily available state. STM is stored in distributed regions across cortex, but frontal cortex and parietal cortex is especially responsible for modulating these representations. Working memory (< 30 s) is closely related to short-term memory, but this concept places more emphasis on active manipulation of information in addition to passive maintenance. Long-term memory can retain information indefinitely and is divided into explicit and implicit memory. Explicit memory requires the hippocampus and medial temporal lobe but is stored in distributed regions across cortex. Different forms of implicit memory require various structures: the neocortex for priming, the striatum for skills and habits, the amygdala for learned fear, the cerebellum for learned motor skills, and spinal reflex pathways for nonassociative learning such as habituation and sensitization. (0.3 pt) 7