L6 - neural circuits of object recognition Flashcards
where is the lateral genicleate nucleus found
in the Dorsal thalamus
where do the LGN neurons recieive signal input from
retinal ganglion cells
what does the LGN give rise to
axons that project to the primary visual cortex
does much integration occur between ganglion cell axons and LGN projection neurons
NO as they make 1:1 connections
what percentage of synaptic input from the cortex is regulated by the LGN and why
60% as it contains lots of interneurons so processing is happening
what are the 2 main pathways in the cortex
ventral - what is an object
dorsal - where is an object
outline the positioning of the ventral stream
starts at V1, goes onto V2 and V4 and then terminates in the inferior temporal cortex
outline the layers of the LGN
6 layers
2 layers receive input from magnocellular ganglion cells
4 layers receive input from the parvocellular ganglion cells
what does each layer have
monocular input - receives input from ganglion cells in one eye only
what happens to complexity of responses of neurons along the ventral stream
increases in complexity
what do lesions in the inferior temporal cortex cause
decreased ability to recognise objects
where does the processing happen
in the cortical layers
features of the cortical layers
layers of neurons
columns (ocular dominance, orientation, direction)
and blobs
what are blobs
involved with processing of colours, different neuronal response dependent on orientation of light
what structure does the cortex have
organised laminar structure
where do ocular dominance columns receive input from
either the ipsilateral or. contralateral eye
outline experiments in which ocular dominance columns can be found
inject radioactive proline in one eye - proline is an aa, is endocytose by ganglion cells, diffused into the LGN neurons. Some goes into the cortex.
inject radioactive glucose into the Cortex and stimulate only one eye with light
difference between different orientation columns
neurons close to each other have different orientations and activies
where do Blob columns receive input from
parvocellular layers of the LGN
what did Hubel and Weisel discover
simple cells respond to a bar oriented in certain direction
where are simple cells localised
layers 4 and 6
what do simple cells respond to
respond to a bar in specific orientations
how do the receptive fields of simple cells differ from receptive fields in the retina and LGN
the simple cells have elongated receptive fields
what determines the orientation of the receptive field of a simple cell
centres of the receptive fields of all neurons projecting to the same simple cell are oriented a long a line
what is the difference between complex and simple cells
complex cell responds to a bar in a certain orientation positioned anywhere in the receptive field
where are the complex cells localised
laters 2, 3 and 5
outline the possible circuit basis of a complex cell receptive field
receives inputs from many simple cells having the same orientation of the receptive field
what is another name for a hypercomplex cell
end stopped cell complex
what do hypercomplex cells respond to
bars in certain orientations
if the stimulus goes away from receptive field, the hypercomplex cell stops resounding
if change orientation of the stimulus outside of the receptive field they start responding again
outline the input and output layers in V1
the simple cells are in layers 4 and 6, send info to higher layers 2 and 3 where some processing occurs. Then the information from the V1 cortex goes to other brain layers - some. back to LGN from lv5
2 properties of neurons downstream of V1
respond to stimuli with a progressively increased complexity
increase in the size of receptive fields
what is a grandmother cell / Jenifer Aniston neuron
neuron responds to images of a particular object in any orientation and scale
same neuron does not respond to other images
outline the population coding model
idea that an object is represented by a large population of cells
problems with the population coding model
poor in scale and orientation invariance
doesn’t take into account feedback from higher cortical areas
need experimental validation, difficult as need to record pre and postsynaptic responses
