3 Representation in the Visual and Auditory System Flashcards
What is the Lateral Geniculate Nucleus (LGN) of the thalamus?
A structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projection of the thalamus where the thalamus connects with the optic nerve.
90% of fibres that originate in the retina and travel in the optic nerve are terminated at the LGN.
LGN Retinotopic Mapping/Organisation
Visual world maps onto the retina and then LGN. Spatial relations are maintained in the nervous system.
Remapping of retinal image onto CORTIAL SURFACE.
Fovel region uses more of V1
Visual Pathway
The visual world –> retina –> LGN –> Primary visual cortex
Simple Cell (V1)
Respond best to elongated bars of light. They can be monocular or binocular.
Are orientation selective
Have on/off subregions
Complex Cell (V1)
Respond to light bar in particular organisation. Nearlly all are binocular (cells in the visual system tasked with providing you with 3D vision or stereopsis, two eyes).
Cell pathway from eye to brain
Retinal Ganglion cell –> LGN –> Simple Cell –> Complex cell.
What does columnar architecture of V1 suggest?
Retrotopic Mapping. The relationship between what happens in space and the visual cortex.
As the electrode put into the brain shifts in V1 the preferred orientation of the neuron changes systematically.
What is cortical mangification?
Cortical magnification refers to the fact that the number of neurons in the visual cortex responsible for processing the visual stimulus of a given size varies as a function of the location of the stimulus in the visual field.
What is retinotopic mapping an example of?
Topographic organisation. An ordered representation of the sensory environment, where spatially adjacent surfaces are represent in adjacent positions in the brain.
Why does our brain use Topographic mapping?
Reduces axon volume (fit more neurons in the brain).
Conserve metabolic resources.
Axon length Is shortest when neurons that share dense connectivity are clustered.
This facilitates processing: e.g. lateral inhibition (opposing processes)
What frequency can humans hear?
20 to 20,000 Hz
Age-related hearing loss. What genders ears fuck out quicker?
Men
How do we hear?
Moving the hair in the ears makes ion channels move which turns auditory signals into electrical energy which the brain can understand.
How is sound represented tonotopically within the Cochlea?
Tones are represented spirally.
Lower tones are apex
Higher tones by the base.
Pathway to the auditory cortex.
Cochlea –> Brainstem –> Midbrain –> Medial Geniculate Nucleus of Thalamus - forebrain –> auditory cortex.
How is the auditory cortex mapped tonotopically?
Ordering of sounds at frequencies
What is top-down processing
Using information from higher-level mental processing and prior experience.
