1. (Neuroanatomy) [3 P]
What anatomical details characterize the (human) cortex?
general layout with 6 layers (with slightly variable thickness depending on the area)
specific cell types in the layers (pyramidal neurons, stellate neurons)
existence of a canonical microcircuit is very likely
general layout with 6 layers (with slightly variable thickness depending on the area) [1 P]
specific cell types in the layers (pyramidal neurons, stellate neurons) [1 P]
2. (Neurophysiology) [3 P]
Membrane channels for ions usually change their conformation depending on specific gating factors. Please name the three basic factors that control the conformation of membrane channels, and shortly describe the mechanism that leads to the opening/closing of these channels.
ligand-gated: binding of a molecule/transmitter changes conformation
voltage-gated: voltage across membrane influences charged groups
mechanically activated (stretch-activated): mechanical forces change conformation
3. (Hodgkin-Huxley Model)
The Hodgkin-Huxley Model for a point-neuron consists of four coupled differential equations. To simplify the dynamics, one can reduce the dimensionality of the model from 4D to 3D. Which component of the model is altered, how is this done, and why is this possible?
(a) The activation dynamics of the sodium channel is simplified.
(b) To do so, the differential equation τm(V ) dm dt = m∞(V (t)) − m(t) is replaced by the algebraic equation m(t) = m∞(V (t)).
(c) This approximation is feasible because for all membrane potentials the time constant τm(V ) is much smaller than the other three time constants of the Hodgkin-Huxley model, i.e., τn(V ), τh(V ) and τRC .
4. (Synaptic dynamics and plasticity)
In class, we discussed the study of Tsodyks and Markram (PNAS 1997). What are the main take-home messages concerning synaptic transmission, synaptic plasticity and constraints for neural coding?
(a) The paper shows that the studied synapses exhibit synaptic depression so that their postsynaptic effect cannot be described by a single synaptic-strength parameter.
(b) The synapses exhibit long-term potentiation of the “use-dependent efficacy” (which can be interpreted as the neurotransmitter release probability) but not of the “absolute efficacy”, as might have been expected.
(c) This phenomenon provides a constraint for firing-rate codes and shows that synaptic dynamics can effect neural coding properties.
Name reasons why it's often difficult to model the brain
Assign words to definitions
Afferent neuron
Nucleus
Brain
Dendritic Spines
Corpus callosum
What are characteristics of the Sodium-Potassium Pump?
does not need energy
ATP induces conformation changes
It is influenced by charge
What does the Goldmann equation describe?
Actual membrane potential of the cell
No ion conductances considered
Equilibrium potential over time
Potential of an ion
Massive Complexity
Recurrent and Dynamic Activity
Distributed and Redundant Coding
Why is the compression a log function ?
Draw Interleaved Sampling Diagram
Indicator and prerequisite for having a Cochlear Implant
The Auditory System Responds Logarithmically to Intensity
The cochlea and auditory neurons respond to sound pressure levels (SPL) over a huge dynamic range (from ~0 dB to 120 dB SPL).
However, neurons have a limited firing range — they can’t represent this full dynamic range linearly.
So, the perceived loudness of sound grows roughly logarithmically with physical intensity (Weber–Fechner law).
deaf and hard-of hearing
7. (Spatial cognition) [3 P]
Inertial sensors, such as the otolith organs in the inner ear of vertebrates, cannot distinguish between gravity and linear acceleration. Nonetheless, we rarely misperceive linear accelerations as body tilt or vice versa.
(a) Give an example where we perceive linear acceleration as body tilt.
(b) The problem is solved by our brain by taking into account other information from another sensory modality. In the absence of vision and sound, which sensory information is used? Which sensor is measuring it?
(c) Which mechanism has been proposed for this case of multimodal sensor fusion?
(a) On a centrifuge, we perceive centrifugal acceleration as body tilt. Catapult launches of aircrafts are also perceived as body tilt.
(b) Angular velocity/acceleration measured by the semicircular canals in the vestibular system of the inner ear.
(c) Dynamic probabilistic estimation modeled as Kalman filter, particle filter, etc.
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