Neuroanatomy & Neurophysiology

LGN

Optic projections from the two eyes remain segregated.

Ipsilatereal Inputs to LGN Layers

2,3 & 5

Contralateral inputs to LGN Layers

1,4 & 6

Where does the LGN terminate?

In the alternating ocular dominance columns in V1 layer IVC of the SAME SIDE.

Where are the Ocular Dominance columns most clear & distinct?

IVC layer of V1

Binocular neurons are found where?

Just outside layer IVC of V1.

Fine Steropsis along the vertical midline

Nasotemporal overlap(bilateral projection)

Coarse Stereopsis along vertical midline

Fibers crossing in the corpus callosum.

Ocular Albinism Evaluation with VEP

Normal= monocularly evoked potentioals show little asymmetry

Albinos= indicates anomalous optic projections

Ocular Albinism Evaluation with fMRI

displayed a marked asymmetry of visual response to full-field stimulation

T0 Neurons

1. responses peak at/about zero
2. Narrow & symmetrical profiles= excitatory & inhibitory
3. Fixation maintence to help maintain vergence accuracy
4. Stereoacuity(any differnce in disparity from zero will cause a BIG change in response of theses neurons)

TN & TF Neurons

1. increased response over a narrow range of disparities of ONE direction (crossed/uncrossed)
2. Excitatory component= TN crossed or TF uncrossed
3. Inhibitory at Zero disparity
4. Vergence Initiation
5. Fixation Maintance

Reciprocal NE & FA Neurons

1. increased response to stimuli having a WIDE range disparites in ONE direction(crossed/uncrossed)
2. Vergence Initiation

V2 Disparity-selective Neurons

1. Cytochrome oxidase staining reveals THICK & THIN stripes & interstripe regions
2. Higher % of disparity-selective neurons
3. Clusters of disparity-selective neurons are found V2

Middle Temporal Cortex, V5

1. motion in depth
2. Motion parallax
3. Stereoscopic vision

Cortical Disparity Encoding

A given binocular cell in the cortex has a receptive field in each eye.

Position Disparity Encoding

1.Centers of RF of simple cells for the two eyes do not precisely align , but are horizontally displaced w/respect to each other.

2. Highest firing rate when stimulus falls on the right & left RF that have horizontal offset of the position of their RF centers

Phase Disparity Encoding

Centers of RF of simple cells for the two eyes are aligned, but PROFILES of their ON-OFF regions are horizontally displaced w/respect to each other.

2. Highest firing rate when stimulus falls on the right and the left RF that have horizontal offset of their response profiles