Download Brain Architecture and Function Parts Size and Cognition

Brain Architecture and Function
Parts
Size and Cognition
Length of human gestation
Q: What limits gestational age?
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Hypothesis I: Obstetric Dilema
1. Childbirth is difficult and risky
2. Humans born born
with brains ~30%
adults size
Chimps ~40%
Human bipedalism constrains brain
size, limited gestation time
“You can’t give birth to a large-brained infant and walk on two legs trouble free . . . “
M. Zuk
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Q: How does homonid locomotion differ from the other great apes?
Q: How might differences in locomotion affect gestational age?
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Hypothesis II: EGG
Humans have huge babies!
Energetic and metabolic constraint
on fetal Growth and Gestation
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Q: In what way has paedomorphosis been important in human evolution?
Brain Architecture
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Q. How’d we get to this point?
Evolutionary trends
Hindbrain: relatively smaller
Midbrain: relatively smaller
Forebrain: relatively larger
especially the cerebrum
(neocortex)
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Brain organization
DEVELOPMENT
• Prosencephalon
– Telencephalon
(cerebrum)
– Diencephalon (eyes,
pituitary, hypothalamus,
thalamus, epiphysis)
• Mesencephalon
• Rhombencephalon
– Metencephalon (pons,
cerebellum)
– Myelencephalon
(medulla)
FUNCTION
• Forebrain
– Cerebrum
– Thalamus
– Hypothalamus
• Midbrain
• Hindbrain
– Pons
– Medulla
– Cerebellum
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Medulla oblongatta
– Highway of axons to/from brain
– Nuclei (cell bodies) that control
autonomic functions
• breathing
• heart rate
• blood pressure
• swallowing
• coughing/sneezing
– Damage is usually fatal
Most cranial nerves emerge
from brain stem
Hindbrain
Hindbrain
Pons (“bridge”)
– On top of brain stem
– Connects cerebral hemispheres with
contralateral hemispheres of cerebellum
– Wakefulness and alertness
– Damage can lead to sleeplessness or
hyperalertness
Hindbrain
Cerebellum (“little brain”)
– As many neurons as rest of brain!
– Monitors sensory input from body and
coordinates with outgoing motor
commands from cerebrum
– Gross motor function
• Posture/balance
• muscle tone
• coordination
– Damage leads to loss of control on
contralateral side
Midbrain
– Connects brainstem to forebrain
– Has nuclei that coordinate/integrate
body movements with forebrain
(damage -->Parkinson’s)
– Eye movements (sup colliculus)
– Pain (Periaqueductal gray region, PAG)
– Reward, addiction, movement
(Substantia nigra)
– Motor coordination (red nucleus)
Small in mammals
Diencephalon
Thalamus (“inner chamber”)
- relays all sensory information to cerebrum (except smell)
- Also involved in awareness & learning
Hypothalamus
- Controls release of hormones by pituitary gland
- Homeostasis of thirst, heart rate, blood pressure
Forebrain
Forebrain
The cerebrum accomplishes most complex cognitive
functions, especially thinking & awareness
- Receives/processes
sensory information
- Complex cognitive
processes
• Language
• Thinking
• Awareness
• Memory
• Consciousness
• Etc…
Forebrain
Topology of cerebral function
Frontal lobes
– Motor functions or
movements (posterior)
– Memory/recognition
– Emotional regulation
– Motor aspects of speech
Parietal lobes
– Integrate stimuli (e.g.,
vision and balance)
Temporal lobes
– Sensory input from ears
– Visual/word memory
Occipital lobe
– Sensory input from eyes
Forebrain
Limbic system
Cortical/subcortical structures around
brainstem: generation/regulating
emotions; learning
Forebrain
Two hemispheres are linked by the corpus callosum
A thick bundle of myelinated axons
Phineas Gage
A moral man, Phineas Gage
Tamping powder down holes for his wage
Blew his special-made probe
Through his left frontal lobe
Now he drinks, swears, and flies in a rage.
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Brain Size
Q: Does body mass predict brain mass?
Q: How does brain size differ among vertebrates?
Northcutt 2002
Brain Size
Q: Does body mass predict brain mass?
Q: How does brain size differ among vertebrates?
Slope = 1.0
Slope ≈ 0.67
Northcutt 2002
Q: Which mammals have the largest percent of body
mass represented by brain? The largest absolute brain?
The largest EQ?
*
log
brain
mass
*
log body mass
*
Estimating the size of a brain subunit: the neocortex of mammals: 1) rhinal fissure placement
hedgehog
2) cerebral sulcation
tree shrew
monkey
rhinal fissure
Q: What aspect(s) of bird behavior correlate most strongly with a large
telencephalic (≈ forebrain) fraction of the brain?
Burish, Kueh, and Wang. 2002.
Pigeons have a telencephalic fraction of 0.552…..
0.552
Burish, Kueh, and Wang. 2002.
…and can distinguish paintings by Picasso and Monet.
Watanabe et al. 1995
Brain to body connection
Q. How does brain receive and send information?
Signal Transduction
An environmental stimulus
Surface neurons are exposed to an
environmental stimulus
The environmental stimulus generates a
receptor potential If the receptor potential exceeds threshold, it
initiates an AP
Sensory input is relayed to the central
nervous system
Q: How do environmental stimuli initiate APs?
AP to the CNS
Signal Transduction
Q: How do environmental stimuli initiate APs?
See text box, p. 338