cogs143 - CS 143 * Animal Cognition Lecture 4: CETACEAN...

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CS 143 * Animal Cognition Lecture 4: CETACEAN BRAINS On Comparing Brains… - EQ = Encephalization Quotient = Ratio of actual brain mass to expected brain mass of comparison animal, corrected for body size - “Expected brain mass” is calculated as = 0.12 X (Body mass in grams) 2/3 - Others use ratio of cortex to rest of brain, brain to cord, sensory-motor areas to association cortex, etc - Most of these put humans at the top, but all have some counter-intuitive results - e.g. Tree shrew brain is 10% of its body weight; Orca E.Q. less than Amazon River Dolphin - All are designed to assess amount of “excess” brain, beyond that needed to run basic functions - Somehow this should be related to “intelligence”…? - Huge body size of cetaceans tends to throw off such metrics - e.g. Sperm whale (body up to 40 tons) has the largest mammalian brain (7-9000 g) but EQ=.07 - PLUS, absolute brain size matters! - Larger brains, more cells, more connections, more processing capacity - Comparing cetacean brains further complicated by 50million yrs of evolution from land mammals - Difficult to identify homologues , esp in later developing areas like cerebral cortex Overall Brain Size and Shape - Shape globular , gross size HUGE, including expansion of Cerebral Cortex - Size: Tursiops : Body 170Kg Brain 1500g EQ 4.4 - Orcinus : Body 10,000kg Brain 6000g EQ 2.7 - Gorilla: Body 170kg Brain 500g EQ 1.8 - Homo : Body 85kg Brain 1000g, EQ 7.5 - Riverine dolphins 200-400 g EQ ranges 1.8-3.5 - Asymmetrical - Right hemisphere larger - Dominant?? Some cognitive data: right dominant for global/spatial/emotional - Acoustic mechanisms asymmetrical (larger on right); Right side of skull also larger Brain Development - Unlike altricial Primates (esp Humans) cetaceans are precocial (well developed) at birth - Dolphin: 12 mo gestation (vs. 9 mo Hum, 8 mo apes) - Brain 40% adult at birth (vs. 25% in Hum) - Due to impedance match of seawater and amniotic fluids, fetus receives continuous auditory input - Possibly contributes to extensive development of acoustic processing by brain Cerebellum - Enormous , largest (absolute and relative size) of any mammal (Tursiops:
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cogs143 - CS 143 * Animal Cognition Lecture 4: CETACEAN...

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