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.