Cognitive Neuroscience: 1999 Admission Exams

English is the language preferred by the Commission. Italian may be used if absolutely necessary. Please write clearly. Please answer three (3) of the following questions:
(1) The Web is now thought to include some 800 million units (documents), whose local connectivity (number of links per document) follows a power law distribution: roughly 1/100 documents have more than 10 links, 1/14,000 more than 100 links, 1/2,000,000 more than 1,000 links. The "informational diameter" of the Web (mean shortest number of links to follow in order to go from one document to another) has been recently estimated to be 19. On the other hand, the human Cortex has been estimated to include some 8 billion units (pyramidal cells) whose local connectivity follows a unimodal distribution, peaked at, say, 40,000. Assuming half of these connections to be really local and half long-range, and both random, produce a back-of-the-envelope estimate of the informational diameter of the Cortex.
(2) As a solitary lighthouse watch on the Fair Isle, you have devised an efficient system to broadcast lyrics and ballads to poetry-avid seafarers: you apply a red, blue or yellow filter (or no filter) at every sweep of the light (3 per minute). Please tell us the code you have used, and how long it took you to broadcast William Wordsworth's "She Dwelt Among the Untrodden Ways" (351 characters including blank spaces).
(3) Discuss the proposal that neuronal activity is involved in the development of sensory cortex, including reference to the possible role of neurotrophic factors.
(4) An axonal fiber branches and contacts a given postsynaptic cell at n synaptic release sites, each of which has an independent probability p of actually releasing a single vescicle of neurotransmitter after a presynaptic spike. The fiber carries spikes with a certain constant probability q per msec (a Poisson process of mean rate 1000 x q Hertz). If the postsynaptic signal decays away with time constant T, in which situation would you regard the variability of the signal as mainly spatial rather than temporal in nature? What if n=100, p=0.1, q=0.01, T=10 msec ?
(5) A 1 mm-diameter column of cerebral cortical tissue contains about 10,000 neurons, arranged in layers, forming something like 1 billion synapses.
(i) What are the basic operations carried out by a cortical column?
(ii) Localization of function is a fundamental principle of cerebral cortex.
Are the functional diffferences between cortical regions due to differences in the operation of the columnar units that comprise them? Alternatively, if the columnar units function in a similar manner, what might account for cortical functional specializations?
(6) Discuss the proposal that different mechanisms of synaptic plasticity (LTP, LTD) are involved in experience-dependent modifications of sensory cortical circuity.
(7) People suffering from motor neuron disease or spinal cord injury would benefit from a technology that would utilize brain signals to control external devices, such as a joystick. Suppose that you have access to neuronal activity recorded at 100 electrodes, implanted chronically in the hand/arm region of primary motor cortex. Describe how you would "decode" this neural activity to control an external device in realtime.
(8) Briefly describe the physical basis of EEG recording.
(9) How would you design EITHER a functional imaging or a neuropsychology study to obtain theoretically useful information on one of the following:
(i) category specificity in semantic memory
(ii) apraxia
(iii) the phonological route in reading
(iv) apperceptive agnosia
(10) Briefly discuss the main advantages and disadvantages of current brain imaging techniques.
(11) Briefly describe an experiment to investigate whether, at birth, the functional properties of the cortex in human infants are organized like those of adults.
(12) Consider the advantages and disadvantages of individual case studies and group studies, for drawing inferences about theories of the organisation of brain processes underlying cognitive disorders manifest in EITHER
(i) adult neuropsychological patients or
(ii) children with cognitive developmental disabilities.
(13) Linguists have developed sophisticated models of grammar. Imagine that the grammar of language X is known. Discuss how it relates to psycholinguistic models of how X is acquired, produced and perceived.
(14) What is the use of brain-imaging to study questions that cognitive science is investigating, e.g., the development of language and thought, the nature of cultural differences, and the origin of individual variation in competence?
(15) Briefly describe the main cortical streams involved in the processing of incoming visual information.
(16) Discuss for EITHER
(i) executive or
(ii) memory processes,
whether they are carried out by a single unitary system, by a number of subsystems in combination or by a number of relatively independent systems. Consider one neuropsychological or neurodevelopmental syndrome with respect to this theoretical issue.