Leah Militello, class of 2018

Transcription

1 Leah Militello, class of 2018

2 Objectives 1. Describe the general organization of cerebral hemispheres. 2. Describe the locations and features of the different functional areas of cortex. 3. Understand the basis of functional imaging. 4. Describe the 3 categories of fibers used for cortical communication and the effects of lesions to them. 5. Understand the concepts of cortical layers and columns. Chris Cohan, Ph.D. Dept. of Pathology/Anat Sci University at Buffalo

3 What Are We Doing Today 1. The Cortical Landscape structural features functional features 2. Communication Paths

4 Significance - Cerebral Cortex Brainstem provides basic survival functions by controlling respiration/cardiovascular function Cortex - the location of conscious awareness of self Provides the capability for: Sensory perception Initiation of voluntary movement - behavior Cognition (thought, emotion, judgment, problemsolving, memory)

5 1. Topography - Cerebral Hemispheres Composed of: Cortex - Grey matter: outer region of cell bodies White Matter: Inner nerve fiber region Deep nuclei buried caudate putamen globus pallidus amygdala From Katalin Hegedus

6 1. Topography - Cerebral Hemispheres Cortex is integrative because it contains cell bodies that receive, process, and communicate information. Underlying white matter -contains axons- transmits information and interconnects areas. Lesions in either location cause sensory, motor, cognitive deficits.

7 1. Topography - Cortical Folding The highly folded cortex allows a very large surface area of cell bodies to be packed into a small space. Cortical surface area differs with species. Mouse Cat Monkey Human

8 1. Topography Gyri, Sulci, Fissures and Lobes on: Lateral, Medial, Inferior Surfaces Hidden Surfaces Insula

9 1. Topography - Location In 1900, Brodmann surveyed the cortex histologically and designated 52 different areas. histological differences indicate differences in processing information and functionality.

10 2. Functional Organization How was this information obtained: Animal Studies Brain Trauma Studies Brain Stimulation during neurosurgery PET (positron emission tomography) fmri (functional magnetic resonance imaging)

11 Functional Imaging Based on the property that neuronal activity causes increased metabolic demands and localized increases in cerebral blood flow or PET measures changes in cerebral blood flow metabolism via short lived isotopes. fmri changes in cerebral blood flow based on how hemoglobin/o 2 affects protons. Require image averaging and statistical comparisons the brain is always active so when a particular task is tested, which active area is responsible? visual stim

12 2. Functional Organization Cortex has a Modular design. Each region has unique structure unique processing of information unique function Lesions cause specific symptoms

13 2. Functional Organization Each area mediates specific function FEF motor tactile These are called primary areas, closely related to sensory and motor pathways. auditory visual What about the other areas not labeled here?

14 2. Functional Organization Other cortical areas: motor tactile Sensory/Motor Association Areas adjacent to primary areas with more complex processing for higher level features (eg stereognosis). auditor y visual prefrontal Integrative Association Areas intervening areas that allow integration of information from different functional areas (eg reading). tactile/visual/auditory

15 2. Function - variability The pattern of cortical folding varies from one brain to another, so it is not possible to know with certainty where a specific function resides on the surface of one person s cortex. Neurosurgeons map this electrophysiologically.

16 2. Function - Cortical Maps Amount of cortex devoted to function depends on significance Sensory - receptor density Motor - need for fine control of muscle Vision - fovea Motor Somatosensory Visual

17 3. Cortical Communication How to get from here to there and back again Association fibers Projection fibers Commissural fibers Deep Axons

18 Diffusion Tensor Imaging MRI can detect and distinguish tracts in white matter based on the direction water diffuses along axons longitudinally. Bundles of fibers that run in different directions give different signals in DTI, which can be detected and separated.

19 3. Communication - Association Fibers Interconnect cortical areas in one hemisphere. Short interconnect adjacent gyri; important for communication within an area Long interconnect more distant areas; distant communication

20 3. Communication - Association Fibers Location: deep in white matter uncinate fasciculus temporal/frontal lobes cingulum temporal/frontal lobes superior longitudinal fasciculus frontal/parietal/occipital/temporal lobes

21 Conditions that damage white matter of the hemispheres (MS, PML, AIDS, head trauma/diffuse axonal injury) can interrupt association fibers and cause cognitive deficits.

22 3. Communication - Projection Fibers The input and output fibers of the cortex to other areas of the CNS. Examples: corona radiata internal capsule thalamocortical fibers corticospinal fibers Damage to these fibers (trauma, MS, infarct) results in major sensory or motor deficits.

23 3. Communication - Commissural Fibers Interconnect cortex of the right and left hemispheres. 3 cerebral commissures: corpus callosum anterior commissure hippocampal commissure Damage to callosum does not result in obvious functional deficits unless tested specifically for them! genu body splenium

24 4. Cortical Connectivity Neocortex has 6 layers. I II III IV V VI Input Input/Output Input/Output Input- sensory paths from thalamus Output to brainstem/spinal cord Output to thalamus Organization of layers is essential for information processing. Developmental problems can cause seizures, mental retardation, or cognitive deficits.

25 4. Cortical Connectivity Complex dendritic arbors allow cells to integrate information across layers. Dendrites expand and retract in response to activity. Increased environmental stimulation causes dendrite expansion with more potential for connections, allowing the brain to adapt to how it is used.