Visual system 5

Visual system 5

1. Studying vision requires complex approach

   • Methods
     • Psychophysical methods and illusions
     • Lesions and other ways to silence neurons or parts of the brain
       • Directed (animal models)
       • After strokes and other neurodegenerative diseases
       • E.g. LM
     • Anatomical studies and morphology (to study connections between neurons)
     • fMRI, electrophysiological recordings and imaging
       • fMRI is a good way to study brain areas involved in visual processing
         • Read about fMRI
       • electrophysiological recordings
         • In vivo
         • Slices
         • Cultured neurons (only for molecular mechanisms)
         • Patch clamp
     • Modeling and theoretical simulations
   • Model organisms
     • Humans
     • Primates
     • Lower mammals (cats, rodents)
     • Lower vertebrates (zebrafish)
     • Invertebrates (Drosophila)
   • Looking to answer questions like...
     • Which part of the brain is involved in a particular processing?
       • Lesions
       • Whole brain imaging techniques
       • Multi-electrode recordings in different brain areas
     • What is the circuit mechanism?

2. Consider a problem

   • mechanism of simple cell receptive field
     • How to validate experimentally?
       • Solution 1: record the activity of the simple cell and many presynaptic neurons one by one
       • Solution 2: image the activity of large populations of neurons simultaneously
       • GCaMP3 reports changes in neuronal calcium concentration and, therefore, neuronal activity
         • Benefits
           • Recording the activity of many neurons
           • Can record simultaneously the input and the output of a particular neuron (circuit reconstruction)
           • One can easily target particular neuronal types(e.g. glu-ergic and GABA-ergic)

3. Stimulation of neurons

   • By light
     • Neuronal stimulation by light : Channel rhodopsin
     • Hyperpolarisation by light: halorhodopsin
   • Blindness and stimulation of visual neurons
     • Retinitis pigmentosa
       • Retinal degeneration
     • Artificial retina

4. Artificial retina

   • See internet images on ppt
   • What part of the brain to activate?
     • Retina (mostly for retinitis pigmentosa)
     • Visual cortex (when the optic nerve didn’t develop or is destroyed)
     • Why is it important to activate as early (anatomically) as possible in the visual pathway?
       • Retina performs complex computations
       • Different ganglion cells have different functions and project to different brain areas
       • Stimulation of RGC with simple stimuli is useless (e.g. motion sensitive RGC is active only when there is motion)
   • How to activate?
     • Electric stimulation
     • Channelrhodopsin (activation by light)
   • Problems
     • Stimulates RGC not photoreceptors or bipolar cells

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