Last Lecture http www umich edupsycours345 Orientational Terminology

Last Lecture http: //www. umich. edu/~psycours/345/ Orientational Terminology Gross Neuroanatomy Cytoarchitecture

Today’s Lecture Cytoarchitectonic and projections maps Plasticity of maps- Phantom limbs Perimetry- measuring deficits of visual sensation Organization of the Visual System Intro to Blindsight

Cytoarchitecture Gray matter is 2 mm thick. 6 layers differing in connections & size, density of cell types. 2 & 4 : receiving layers 3, 5 & 6: sending layers fibers from sensory and association cortex thicker in sensory cortex 3 - association cortex and commissures 5 - brainstem and spinal cord 6 - thalamus thicker in motor cortex Thalamocortical, corticothalamic & Corticocortical connections (intra and interhemispheric)

Cytoarchitectonic Maps: Complex micro-structure of neural tissue Brodmann's (1909) Map Classified regions based on cell layers Identified 52 areas Structural classification --> functional differences system widely used to refer to areas of interest.

Projection Maps defined by their input What gets mapped depends on the sensory modality vision-- visual space auditory-- pitch (frequency) touch-- body surface

Properties of Cortical Organization Hierarchical Organization ranking based on modality specificity & complexity of functions Contralateral Organization Left Hemisphere represents: Right Visual Field Right side of body Right Ear Input Vice versa for Right Hemisph. Functional Segregation “modules” with specialized functions Generic (simplified) Pathway: SENSORY RECEPTOR THALAMIC NUCLEUS PRIMARY CORTEX SECONDARY CORTEX ASSOCIATION CORTEX

The Body is Mapped onto the Brain

A Closer Look at a Projection Map: Stimulation studies of Penfield The Sensory Homunculus: body surface mapped onto cortical surface (AREA 3) Important Principles: the map is orderly somatotopic organization: adjacent body regions are adjacent on the cortex amount of dedicated cortex reflects sensitivity of the body surface Motor Homonculus mapped onto Area 4

Experience/Nurture can alter the maps Surgical manipulation of fingers leads to decreased resolution of sensory map.

Experience/Nurture can create phantom phenomena. . .

Cortical Reorganization Sensory input is missing for hand area. Cells in face area takeover hand area. Stimulation of face now activates hand area. This gives rise to sensation of a phantom hand. (V. Ramachandran)