L6 - neural circuits of object recognition

Question 1

where is the lateral genicleate nucleus found

Answer 1

in the Dorsal thalamus

Question 2

where do the LGN neurons recieive signal input from

Answer 2

retinal ganglion cells

Question 3

what does the LGN give rise to

Answer 3

axons that project to the primary visual cortex

Question 4

does much integration occur between ganglion cell axons and LGN projection neurons

Answer 4

NO as they make 1:1 connections

Question 5

what percentage of synaptic input from the cortex is regulated by the LGN and why

Answer 5

60% as it contains lots of interneurons so processing is happening

Question 6

what are the 2 main pathways in the cortex

Answer 6

ventral - what is an object

dorsal - where is an object

Question 7

outline the positioning of the ventral stream

Answer 7

starts at V1, goes onto V2 and V4 and then terminates in the inferior temporal cortex

Question 8

outline the layers of the LGN

Answer 8

6 layers
2 layers receive input from magnocellular ganglion cells
4 layers receive input from the parvocellular ganglion cells

Question 9

what does each layer have

Answer 9

monocular input - receives input from ganglion cells in one eye only

Question 10

what happens to complexity of responses of neurons along the ventral stream

Answer 10

increases in complexity

Question 11

what do lesions in the inferior temporal cortex cause

Answer 11

decreased ability to recognise objects

Question 12

where does the processing happen

Answer 12

in the cortical layers

Question 13

features of the cortical layers

Answer 13

layers of neurons
columns (ocular dominance, orientation, direction)
and blobs

Question 14

what are blobs

Answer 14

involved with processing of colours, different neuronal response dependent on orientation of light

Question 15

what structure does the cortex have

Answer 15

organised laminar structure

Question 16

where do ocular dominance columns receive input from

Answer 16

either the ipsilateral or. contralateral eye

Question 17

outline experiments in which ocular dominance columns can be found

Answer 17

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

Question 18

difference between different orientation columns

Answer 18

neurons close to each other have different orientations and activies

Question 19

where do Blob columns receive input from

Answer 19

parvocellular layers of the LGN

Question 20

what did Hubel and Weisel discover

Answer 20

simple cells respond to a bar oriented in certain direction

Question 21

where are simple cells localised

Answer 21

layers 4 and 6

Question 22

what do simple cells respond to

Answer 22

respond to a bar in specific orientations

Question 23

how do the receptive fields of simple cells differ from receptive fields in the retina and LGN

Answer 23

the simple cells have elongated receptive fields

Question 24

what determines the orientation of the receptive field of a simple cell

Answer 24

centres of the receptive fields of all neurons projecting to the same simple cell are oriented a long a line

Question 25

what is the difference between complex and simple cells

Answer 25

complex cell responds to a bar in a certain orientation positioned anywhere in the receptive field

Question 26

where are the complex cells localised

Answer 26

laters 2, 3 and 5

Question 27

outline the possible circuit basis of a complex cell receptive field

Answer 27

receives inputs from many simple cells having the same orientation of the receptive field

Question 28

what is another name for a hypercomplex cell

Answer 28

end stopped cell complex

Question 29

what do hypercomplex cells respond to

Answer 29

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

Question 30

outline the input and output layers in V1

Answer 30

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

Question 31

2 properties of neurons downstream of V1

Answer 31

respond to stimuli with a progressively increased complexity

increase in the size of receptive fields

Question 32

what is a grandmother cell / Jenifer Aniston neuron

Answer 32

neuron responds to images of a particular object in any orientation and scale
same neuron does not respond to other images

Question 33

outline the population coding model

Answer 33

idea that an object is represented by a large population of cells

Question 34

problems with the population coding model

Answer 34

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