Philosophy of neuroscience Flashcards
(29 cards)
What is understanding?
Problem is there is no formalised definition.
Selveston proposed: when all the components, connections and their properties are defined.
* Incomplete since ‘component’ is not defined.
This means we are essentially chasing a moving goal.
What are the main properties for ideal technology?
Whether structural, observational or functional:
* Keeping a high resolution (temporal/spatial) increasing capcacity
* Reporting accurately (not using a proxy)
* Recording without altering function
* Manipulating without off-target effects.
Even if we had ‘ideal’ technology, what are the fundemental barriers to full understanding?
Variability between individual components and individuals:
* We know it exists
* Fundementally limits how much measurement in one system cna be applied to another
Variaiblity in time (plasticity):
What is the point of understanding (Godel)? What are the main strategies to increase it?
Point of investigation is to increase accuracy of model for prediction. Understanding is a tool to acomplish this NOT a goal in itself.
* Godel’s incompleteness theorem came to a similar conclusion
Given understanding is a useful tool - how do we increase it?
* Reductionism, understanding individual components better
* Holism, understanding whole system function together
* Technology is useful in both these approaches.
Will we ever reach ‘complete’ understanding of neural circuits?
(Understanding is not a goal in itself, but a tool).
Therefore we will not ever reach full understanding (due to variability, off-target effects of technology) BUT we may reach significant understanding, with robust and precise predictions good enough for use in our purposes (e.g. in treatment)
What is Godel’s incompleteness theorem?
‘A consistent system, despite an effective procedure will not be able to prove all truths about itself’.
To what extent are neural networks understandable? (Basic essay plan)
- What is understanding? I.e. what is the point → tool for prediction
- How do we attempt to understand? Reductionism and holism together due to limits of technology (resolution vs. capacity problem).
- Even with ideal technology, will there are still limits to understanding → Variability, plasticity
Why is holism needed?
Holism provides understanding of how the whole system functions
* Emergent properties (possessed by the whole system but not individual parts e.g. ephapses)
* Essential in highlighting where reductionist approach is inconsistent/less translatable.
Why is plasticity a fundemental limitation to understanding?
Plasticity is essentially variability in time.
* Output altered depending on input
* Measuring becomes part of that history (current technology still has some effect on function)
* Therefore repeat experiments are not identical
* Therefore how do get reliable data or standardise across findings for a model?
What is Moore’s law?
Computational power increases exponentially while cost decreases over time.
Why is reductionism useful?
Allow more accurate investigation into the function of one component.
* E.g. isolating a neuron means the stimulus can be controlled and recording from easier
* If embedded in a network, there are too many variables to measure (e.g. can be receiving ephaptic inputs)?
* Well controlled parameters increase validity of experiment but decrease realism of model.
Problem is that this may not represent how the component acts within the system.
What are emergent properties?
Properties which are only seen when a system is whole:
* Limit to reductionism
* Ephapses are good example
What is diaschisis?
Phenomenon of functional changes in a distant sight to the one being manipulated.
Why might variability in experimental data be more important than previously thought?
Variability may not be a consequence of the experimental process, but a fundamental property of the system
What are the three types of variability which can explain variability in experimental data?
Systematic variability: caused by errors in experimental conditions (e.g. parameter which is thought to be controlled is actually fluctuating and impacting measurements)
Measurement variability: variabiltiy due to uncertainty in tool use
Natural variability: inherent randomness of the system.
What is Ashby’s law of variability?
‘When variety of the environment exceeds capacity for variety of a system, the environment will dominate and ultimately destroy that system’.
Argument for the necessity rather than just presence of naturla variability
Why are Lamprey useful models for simple neural circuits?
Most primative vertebrate to have a neural crest during development.
Spinal cord can survive outside the body.
What is Wiener’s famous quote about the best model?
“The best model for a cat is another cat, or preferably, the same cat”
What is the Simpson’s paradox?
Phenomenon where a trend appears in data which is reversed or disappears when sub-groups are looked at.
(http://en.wikipedia.org/wiki/Simpson%27s_paradox)
Can lead to improper identification of correlational relationships.
What are the two major assumptions that observation techniques are beholdent to?
- That the act of observing does not alter the function of the system
- That the resported values are representative of the actual values (e.g. is a proxy for function being used such as Ca2+ for voltage or BOLD signal for activity level).
These assumptions impact the validity of some techniques more than others.
What are the two main caveats to results from optogenetics?
That optogene is expressed in the relevant neurons and only those neurons:
* Failure to evoke an effect may suggest a component is not necessary when it actually involved but has not be activated (omission error)
* Evoking an effect may suggest sufficiency when that component is irrelevant and result is from off-target effects. (Comission error
That optogenetic activation mimics physiological activation
What is the limitation in interpreting strength of connection studies from anatomical tracing?
‘Net strength’ diagrams often quoted based on anatomical tracing (more connections = stronger functional connection)
However:
* Strength of each synapse not known
* Direction not known
* Indirect connection influence not known
Give an example where investigation has revealed heterogeneity:
- Parra et al 1998: 16 distinct functional groups found in CA1 area of hippocampus which were previous grouped together
- Immune diversity e.g. 100s of TAMs found in cancer - very important for targeting during treatment
How did Olsen and Wilson argue there is a direct synaptic connection between two neurons? What are the problems with this?
“If a precisel timed depolarisation of one neuron evokes a short-latency synaptic response in the other, the direct connection is unequivocal”
Problems:
* Some monosynaptic connections are slow…Some polysynaptic are fast…therefore not unequivocal
* Electrical or ephaptic synapses!
