The Brain in MRI and CT

•MRI are taken by a rotating magnetic field

• CT scans are taken by rotating X-ray source

Always Your Right is the Patient’s Left

You

Coronal

Axial

You

Patient

Patient

In axial MRI , you looking from down to top, as if you look to the patient from the feet “see demonstration”In coronal MRI, you looking to the patient face to face.

Ventral “What” pathway

Ventral “What” pathway

• Carries information about static object properties such as colour, luminance, stereopsis and pattern recognition.

• Slow pathway from P-ganglion cells (through laminae 3-6 of LGN, V1) to V2, V4 and inferior temporal cortex

Dorsal “Where” pathway

Dorsal “Where” pathway

• Information about dynamic object properties- motion and spatial

relationships

• Fast pathway for transient visual signals

• Pathway to V1, V2, MT, medial superior temporal and parietal lobe

David van Essen

Visual processing of information

Damage to “What” pathway

Achromatopsia, agnosia

Achromatopsia

• Complete achromatopsia- BL

area V4: Lingual/fusiform

gyri/occipitotemporal junction

Color agnosia

• Color agnosia: loss the ability

to retrieve color knowledge

• cannot name colors for objects

but can sort

• Remembering the color of

object

• Color composition

Left or bilateral occipitotemporal region Inferior temporal , fusiform and right lingual

Color anomia• Inability to name colors or to

point to colors given their names, which is not due to aphasia or due to defective color perception

Color anomia

• Usually associated with left mesial occipitotemporal region

• hence usually affect the visual cortex or optic rediation leading to right hemianopia , and also associated with alexia

• Inability to name colors or to point to colors given their names, which is not due to aphasia or due to defective color perception

The Neural Basis of Visual Perception

• Visual agnosia is the inability to recognize objects despite satisfactory vision.– Caused by damage to the pattern pathway

usually in the temporal cortex. – For words : Alexia

Agnosia

• Topographagnosia– Inability to navigate routes using familiar landmarks -

deficit in familiar scene perception– Right lingual gyrus

• Alexia– Left (dominant lobe) fusiform/lingual areas

Lesion, left occipitotemporal region and involves parts of the lingual and fusiform gyri.

Hemi- achromatopsia , pure alexia , and category-specific visual object agnosia

Occipitotemporalgyri

Occipitotemporalgyri

Kanwisher , McDermott, and Chun, 1997

Kanwisher , McDermott, and Chun, 1997

Agnosia

• Prosopagnosia- – Inability to recognize or

learn faces– Identify people by other

cues- gait, mannerisms or facial features- spectacles, gait

– Aware of defect– BL lingual and fusiform

gyri of medial occipitotemporal cortex.