IUBio

Dolphin brain

Sturla Molden stumol at stud.ntnu.no
Tue Jan 26 11:25:31 EST 1999


who at cares.com wrote:

: But, I can say that humans sleep with onlky "part" of their brain: the
: brainstem (medulla, pons) remeains inherentkly active or indeed
: breathing fails (BPressure etc).

: The "large" in dolfin & primate brain refers mostly to neocortex.
: These are not essential for homeostasis.

It's true that dolphins have unilateral sleep. And if I 
remember correctly, dolphins also have little or non REM 
sleep. The amount of time spent in REM sleep correlate
negatively with neocortical volume.

The mammal with the largest neocortex when the effect of
body mass scaling is removed (that is, neocortical volume
devided by bodymass^0.65) is the Echidna. The Echidna 
(also called the spiny ant-eater) is a monotreme,
i.e. one of the most relictual mammals. For example, the
it lays eggs and lack mammillary nipples. So the
most relictual (primitive) mammal species has the biggest 
neocortex. Interestingly, the Echidna lack REM sleep 
all together.

If I am not wrong, the small amount (none?) of REM sleep
found among dolphins fully explain their enlarged
neocortex. But the functional role of REM sleep remain 
a mystery.  


Sturla Molden



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