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Introduction: Traumatic Brain Injury

Chris Rorden– Overview of course– Motivation and Significance of Topic– Basic terms and anatomy

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Brain function

Brain functions are both distributed and modular. Modular: focal injury can lead to specific impairment.

– E.G. Lanugage deficits typically seen after left but not right hemisphere injury.

Distributed: large network involved– Damage to any nodes or white matter tracts lead to eye movement

deficits.Knock on effects: damage to one node degrades performance

upstream.– Damage to V1 effectively disables V2.

Disconnection syndromes:– Damage to white matter sufficient to disable intact cortex.

Regeneration

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Peripheral nervous system can exhibit profound rehabilitation.

In general, CNS neurons do not regenerate, though glial cells often do.

Neurons can exhibit dendritic sprouting.

Changes in neurotransmitters and blood flow also play a role.

Rivers and Head ~1908

Plasticity

The brain is often able to compensate in response to small injuries.

Most rehabilitation aims to leverage this.Plasticity effects are age related, typically younger

individuals show better effects.Plasticity also changes with time. Injury and recovery

often exhibits a characteristic time course.Plasticity is typically a good thing, but not always.

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Types of Injury

Focal versus Diffuse.– Focal refers to discrete spatial extent,

for example TBI due to mechanical force (vulnerable regions) or stroke due to blockage (ischemic).

– Diffuse refers to widespread injury to many regions. For example TBI due shearing of white matter or stroke due to bleeding (hemorrhagic).

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TBI

TBI classification remains vague.Mild injuries much more common.

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Classification

GCS: Glasgow Coma ScalePTA: Post traumatic AmnesiaLOC: Loss of consciousnessMild TBI Terms

– Complicated mTBI: injury visible in brain scan– Postconcussion injury: long term deficits– Concussion: mTBI ~ brain clearly injured, typically

full functional recovery. Permanent injury debated

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Immediate and long term effects of TBI

Contusion (bruising) results in increased cranial pressure. Brain can herniate. Life or death situation.

TBI also associated with latent effects. Often symptoms get worse with time.

Epilepsy (recurrent seizures) can begin months after injury.

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TBI and age

TBI most common in young and old.Classic ‘Bathtub’ function. Children run into things, do not attend wellAdolescents drive cars and are often addled

by testosterone.Older individuals often fall.

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Reporting findings

How do we describe anatomy to others?– We could use anatomical names, but

often hard to identify.– We could use Brodmann’s Areas, but

this requires histology – not suitable for invivo research.

Both show large between-subject variability.

Requires anatomical coordinate system.

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Ambiguous Coordinates

Human brain rotated relative to spine

Ambiguous dimenstions– Dorsal/ventral– Rostral/caudal

Unambiguous dimensions– Head/Foot– Superior/Inferior– Anterior/Posterior

R C

R CR

C

V

D

V

D

V D

Rat

Human

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Anatomy – Common Terms

Posterior <> Anterior

Po

ster

ior

<>

A

nte

rio

rIn

feri

or

<>

S

up

eri

or

lateral < medial > lateral

Radiological convention: Left on right side Neurological convention: Left on left side

sagittalcoronal

axial

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Brain Coordinates

On Earth: North, South, East and West.– 0˚N/S explicitly defined by spheres rotation (equator).– 0˚E/W arbitrary (Greenwich by convention).

For brain: Left/Right, Sup./Inf., Ant./Post.– Origin of L/R explicitly defined (brain symmetry)– Origin of S/I and A/P arbitrary.

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Coordinates - Talairach

Anterior Commissure (AC) is the origin for neuroscience.– We measure distance from AC

57x-67x0 means ‘right posterior middle’.Three values: left-right, posterior-anterior, ventral-dorsal

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Recognizing the cortical lobes

Cortical lobes: Frontal, Parietal, Occipital Temporal, Insula.N.B. Cerebellum and subcortical gray matter.

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The major sulci

Postcentral easy to find: becomes intraparietal. Precentral easy to find- attached to superior frontal. Between these is the Central (Rolandic).

Interhemispheric fissure

Sylvian (lateral) fissure

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Major sulci

You can usually find the central suclus’ motor hand area (omega shape on axial slice)

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Gyri and sulci

Naming of most gyri (ridges) and sulci (valleys) follows simple pattern of position (superior, middle, inferior) and lobe name.