Why Brains Are Ugly

Let’s face it. . . brains are ugly and complicated looking

And we may be the worst offender!

The problem is that much of the ‘architecture’ of the brain is not

functionally meaningful

FPO

T

F

Santiago Ramon y Cajal

‘…to extend our understanding of neural function to the most complex human physiological and psychological activities, it is essential that we first generate a clear and accurate view of the structure of the relevant centers, and of the human brain itself, so that the basic plan – the overview – can be grasped in the blink of an eye.’

Histology of the Nervous System of Man and Vertebrates (1909)

Telencephalon(or ‘Cerebrum’)

Swanson, 1995

Brain

stem

To Begin, Let’s Break the Brain into Two Functional Parts.

Telencephalon

Cerebellum

Diencephalon

Hindbrain

Spinal Cord

Midbrain Superior Colliculus Inferior Colliculus

CortexLimbic SystemBasal Ganglia

ThalamusHypothalamus

Now add in some sub-divisions

Brain

stem

Brain RegionsYou Should

KNOW

HumanCNS

Swanson, 1995

Tel: 81Di: 4

Mid: 1Hind: 2

Cblm: 10SC: 2

RatCNS

Tel: 38Di: 6

Mid: 4Hind: 7

Cblm: 10SC: 35

81

Zebra FinchCNS

Tel: 64Di: 6

Mid: 10Hind: 6

Cblm: 10SC: 4

PigeonCNS

Tel: 38Di: 6

Mid: 12Hind: 7

Cblm: 11SC: 26

64

Rat Pigeon Finch HumanTelencephalon: 38 38 64 81Diencephalon: 6 6 6 4Midbrain: 4 12 10 1Hindbrain: 7 7 6 2Cerebellum: 10 11 10 10Spinal Cord: 35 26 4 2

S e n s o r y – D o r s a l

M o t o r – V e n t r a l Hypothalamus

Thalamus

The Brainstem has a simple dorsal/ventral organization

Dorsal

Ventral

When they are sick,Some Dogs

Might Vomit

Note the two sub-divisions of the diencephalon: Thalamus and Hypothalamus

RatCNS

TelencephalonStimulus (what), motor control

Thalamusrelay, feedback(except olfaction)

Spinal Cordreflexes, input, output

MidbrainStimulus (where) vision and audition only and orienting responses

PrimarySensory Cortex

PrimaryMotor Cortex

Motor output

Sensory input

GENERAL Overview of

Sensory System Organization

(L/R and R/L crossing for vision, touch, audition

only)

RatCNS

TelencephalonPrimary Auditory Cortex

ThalamusMedial Geniculate

MidbrainInferior Colliculus

HindbrainPons, Medulla

Basal

Ganglia

AmygdalaHippocampus

Cortex

TELENCEPHALONAND

DIENCEPHALON(some key subregions for S&P)

Cortex

Limbic

Basal Ganglia

Thalamus

Hypothalamus

Thalamus

Hypothalamus

Telencephalon

Diencephalon

1

2

3

4

5

6

From Thalamus

Back To Thalamus

Output Layer

CORTEX is made of Vertical Columns, each containing 6 layers of neurons

2D ReceptorArray

Thalamus

Primary Cortex

However…

Dense 2D Receptor Array

Thalamus

Cortex Is‘Modular’

Means the size and density of cortical columns is fixed

Because Cortex is Modular, Sensory ‘Maps’ in Primary Cortex are Distorted by Variation in the Density of Sensory Receptors

A ‘homunculus’ of the USA

Ha-ha! That looks funny!