Cognitive Neuroscience:
Written examination given October, 18, 1995
Please answer three (3) of the following:
- The membrane potential U(t) of a regular-firing neuron follows
approximately the RC equation:
C dU(t)/dt = -g U(t) + C Uo SUM(spikes) delta(t-t(spike));
with C/g = 10 msec; Uo = 0.3 mVolts; and t(spike) the arriving time
of each spike emitted by 100 excitatory presynaptic cells; when U(t) = 20
mVolts the neuron emits a spike and U(t) is reset to 0.
Discuss the spiking activity in the 4 cases:
- the presynaptic cells fire periodically and in full synchrony every 10 msec.
- they fire fully synchronous bursts but at random times, with a constant
Prob(burst) = 0.1 msec^-1.
- each cell fires periodically every 10 msec completely desynchronized
from the others.
- each cell fires at independent random times with a constant P(spike) =
0.1 msec^-1.
- The activity of 10 neurons within a cortical area correlates with the
direction of gaze in the frontal hemispace. Consider at least 2 different
ways in which this population could represent such a 2-D space, and detail
the angular resolution they would provide. If you wish, you may relate
properties of these cells to a given cortical area.
- Discuss the concept of critical periods in the development of brain
functions. Do critical periods relate to general concepts of cortical
plasticity?
- Discuss the anatomical and functional circuitry of one particular system
of learning and memory.
- Synaptic long-term potentiation (LTP) and long-term depression (LTD)
have been proposed as the neuronal bases of learning and memory. However,
almost all experimental evidence has been obtained in conditions where no
real learning and memory occurs: slices of brain tissue maintained in vitro.
Very briefly summarize what is known about the physiological mechanisms of
LTP and LTD. Then propose an experimental design that would allow you to
find out whether synaptic modification really occurs in the intact brain of
mammals during learning.
- Discuss the organization of one mammalian sensory system
- from the sensory receptor to the sensory cortex; OR
- within cortex.
- Create and describe an experiment that could shed light on the role of a
given sensory or motor cortical region in learning a task or behavior. The
experiment can be in an animal species or in humans. Define the
task/behavior carefully. The experiment can be invasive or non-invasive and
should involve at least one of the following methods: electrophysiology,
functional imaging (PET, MRI), ablation.
- Discuss the role of dynamical attractors in recurrent neural networks.
- In the computational modeling of perceptual, memory, or cognitive
processes, how important is it to use elements that are realistic on the
neurobiological level? Answer with respect to any one of the three domains
(perceptual, memory, or cognitive).
- Suggest a model that can address the brain mechanisms underlying object
constancy, namely the way that an object can be identified at different
times even though the exact sensory information changes. Alternatively,
suggest a model that can address some other form of constancy, such as color
constancy. To explain your model it may be useful to choose a specific
example of constancy in one sensory modality (tactile, visual, auditory).
- There are many functions with respect to which the spatial relation
between objects or elements might be computed -- such as control of action,
object recognition, determination of object movement, determination of the
spatial relation between objects. Discuss using computational or empirical
criteria, or both, the different cognitive or neural systems that might be
involved.
- A patient presents with an apparently isolated disorder of face
recognition, with the perception of other categories of visual stimuli being
intact. Would you infer that there was a subsystem in the brain specialized
for the recognition of faces? What investigations would you carry out which
could influence your answer to the question?
Edited by:
Alessandro Treves,
SISSA,
Trieste,
Italy.
ale@limbo.sissa.it