Abstract
With the largest brain in the animal kingdom and its enormous gyrification, the cetacean brain has long been of scientific interest. However, no cetacean species, nor any other large-brained species, has exceeded the human brain in total neuron number in the cortex. For the first time, I present a species that has outnumbered the human brain. Stereological methods were applied to nvestigate three cortices, the entire cortex, and two subdivision of cortex, the auditory and visual cortices, of the long-finned pilot whale (Globicephala melas). The aimwas to estimate the volume of the cortex and to estimate the total number and density of neurons and glial cells in these regions. The long-finned pilot whale has a total of 37.2 x 10**9 cortical neurons and 12.7 x 10**9 cortical glial cells in average. This is almost twice as many neurons in total compared to the human cortex (21.5 x 10**9). However, humans have a higher neuron density (44 x 10**6/cm3) compared to the long-finned pilot whales (30.9 x 10**6/cm3), and have therefore relatively more neurons. The average volume of the cortex was 1209 cm3, and the auditory cortex was significantly (P<0.05) larger in volume (87 cm3) compared to the visual cortex (71 cm3). However no significant difference was in total cell number or cell density between the auditory and visual cortices, even though the whale uses the auditory system as its primary sensory system when navigating and foraging, because they live in an underwater habitat where sight is limited. A significant positive correlation (r=0.8, P=0.005) was between volume of the cortex and glial cell number, indicating that a larger brain requires more glial cells for support.
| Date of Award | 2013 |
|---|---|
| Original language | English |
| Supervisor | Nina Eriksen (Supervisor), Bente Pakkenberg (Supervisor), Maria Dam (Supervisor) & Svein-Ole Mikalsen (Supervisor) |