Optical Sensors Flashcards
What are the advantages and of using microscopy to study neural activity? = 4
- Non-invasive method.
- Depending on magnification and resolution, can study thousands of cells down to individual synapses or axons.
- Capable of imaging multiple fluorophores, with each fluorophore measuring something different.
- Can be combined with optogenetics, electrophysiology, and behavior studies.
What are the disadvantages of using microscopy to study neural activity? = 4
- Considered a proxy measure.
- Requires the insertion of a dye or fluorescent protein into cells, which can affect their function and, in some cases, be toxic.
- Involves technical challenges ranging from light penetration into the brain to fast imaging with sufficient resolution to measure neural signals.
- Expensive and demands strong technical skills for both acquisition and analysis.
What is fluorescence? = 3
- Fluorescence is a phenomenon where a substance absorbs light energy at a specific wavelength and then emits light at a longer wavelength, typically visible light.
- This emitted light is often of a different colour than the absorbed light,
- it occurs almost instantaneously after the absorption of the excitation light.
What is the role of calcium in mammalian neurons, and how is it related to neuronal firing? = 2
- Calcium serves as an important intracellular messenger in mammalian neurons.
- During neuronal firing, the intracellular concentration of calcium increases by approximately 10 to 100 times
How is calcium imaging used to measure neuronal activity? = 2
- Calcium imaging involves capturing the increase in intracellular calcium concentration during neuronal firing.
- This increase in calcium concentration is used as a proxy measure of neuronal activity.
Describe the process by which calcium indicators are used in calcium imaging. = 2
- Calcium INDICATORS which are CALCIUM BUFFERS, fluoresce when they bind free calcium ions.
- When calcium enters or is released into the cell, calcium buffers bind to the free calcium, causing the indicators to fluoresce.
What is the outcome measure in calcium imaging, and how is it expressed?
The outcome measure in calcium imaging is the change in fluorescence, typically expressed as
delta F/F.
What are the limitations of calcium imaging in neuroscience? = 4 AND EXPLANATIONS
- ‘Limited Information on Signal Processing’:
- Calcium imaging provides limited information about natural signal processing in neurons. - ‘Limited Detection of Hyper-polarizing Signals’:
- It offers little to no information on hyper-polarizing signals. - ‘Difficulty in Detecting Subthreshold Depolarizing Signals’:
- Subthreshold depolarizing signals, occurring below the action potential threshold, are challenging to detect. - ‘Difficulty in Separating Fast Signals’:
- Very fast signals are hard to separate from one another using calcium imaging.
What are the applications of calcium imaging in neuroscience? = 5
- Neural Activity Imaging:
- Calcium imaging is commonly used to measure neural activity by detecting calcium signals in the soma. - Synaptic Activity Imaging:
- It can also image synaptic activity by detecting calcium in dendritic spines. - Genetically Encoded Calcium Indicators (GECIs):
- GECIs are commonly employed for neural activity imaging in both soma and dendritic spines. - Combination with Behavior Studies:
- Calcium imaging is often combined with behavior studies to identify neurons involved in specific tasks. - Axonal Activity Imaging:
- It can be used to image axonal activity, including neurotransmitter release and action potential propagation.
What is voltage imaging, and why is it considered an ideal form of neural imaging?
Definition:
Voltage imaging involves capturing changes in membrane voltage in neurons.
— Ideal Form:
It is considered ideal because it can RESOLVE SPATIAL AND TEMPORAL DYNAMICS BETTER THAN OTHER IMAGING MODALITIES
What is the key challenge in voltage imaging, and how is it being addressed?
The main challenge in voltage imaging is ‘MAKING VOLTAGE FLUORESCE’ SO IT CAN BE IMAGED WITH GOOD TEMPORAL RESOLUTION.
Addressing the Challenge:
Genetic voltage indicators involve ATTACHING A FLUOROPHORE TO THE VOLTAGE SENSING DOMAIN ON GENETICALLY MODIFIED ION CHANNEL, OFFERING A SOLUTION TO THIS CHALLENGE.
What are the challenges associated with current voltage imaging methods? = 2
- ‘Dim Indicators’:
Current voltage indicators exhibit low fluorescence changes per millivolt (mV), making them relatively dim. - ‘Specialized Equipment’:
Voltage imaging requires specialized equipment for both excitation and rapid imaging of the fluorophores.
What are the advantages of voltage dyes over genetically encoded indicators in voltage imaging? = 2
- ‘Improved Imaging Capabilities’ :
– Voltage dyes currently offer better voltage imaging capabilities compared to genetically encoded indicators. - Mechanism:
– Voltage dyes incorporate into the neuron membrane, and the fluorescent protein is excited by the change in voltage of the membrane.
What are the characteristics of the best voltage dyes used in voltage imaging? = 2
- ‘Brightness’:
The best voltage dyes are relatively bright. - ‘Fluorescence Change per mV’:
They change by approximately 0.5% per millivolt (mV) of membrane voltage change.
Why might researchers want to image neurotransmitter release in addition to calcium imaging? = 2
- ‘Understanding Release Timing’:
- While calcium imaging indicates neural activity, imaging neurotransmitter release reveals when a neurotransmitter has been released, providing insight into the neural circuit’s function and its relation to behavior or events. - ‘Decoupling Action Potentials and Release’:
The number of action potentials doesn’t always correlate with neurotransmitter release, highlighting the importance of directly observing neurotransmitter release.
