Bob Jacobs et al
Feb 23, 2011Public
Photo: Figure 1: Two cortical regions of the elephant brain (~5,000g) were examined: inferior prefrontal lobe (on the left—note the large size of the olfactory bulb being retracted) and occipital lobe (on the right).
Photo: Figure 2: The primary neuron in the cerebral cortex is the pyramidal cell. In primates and rodents, it appears as in (A), which is from human cortex. Note the singular, ascending apical dendrite highlighted by the arrow. Markedly different in the elephant is an apical dendrite that divides soon after leaving the cell body (B), sending two widely bifurcating apical branches towards the (pial) surface of the brain (red arrow). Most pyramidal neurons in the elephant exhibit this pattern.
Photo: Figure 3: The large image here provides a low magnification view of the occipital cortex in the elephant. Very clearly indicated by the red arrows are an abundance of superficial pyramidal neurons, each with a bifurcating apical dendrite (noted in Figure 2). These apical branches often bundle as they ascended towards the pial surface (small inset images), presumably allowing these neurons to form close, functional units. Note the very spine-rich nature of these branches (spines are the small protrusions on the dendrites that, like the leaves of a tree, increase the surface area of the neuron, allowing for more input to be synthesized).
Photo: Figure 4: A low magnification view of the frontal cortex in the elephant. Remarkable in this photomicrograph is the variety of spiny neuron types: (A) an inverted pyramidal neuron; (B) a “matriarch” neuron (see Figure 6); (C) a smaller, superficial pyramidal neuron; (D) a magnopyramidal neuron; and (E) a fork neuron. This is a greater diversity of neurons than is typically noted in primates or rodents, but appears to be typical of elephants. Note also the large dendritic spread of many of these neurons.
Photo: Figure 5: This is a low magnification view of the occipital cortex in the elephant. Very clearly indicated by the red arrows are an abundance of relatively deep, large neurons (e.g., flattened pyramidal neurons) with very widely bifurcating apical dendrites. These were common in the elephant and suggest a great deal of lateral integration of information, perhaps because of the relatively low density of cortical neurons.
Photo: Figure 6: Represented here is a magnopyramidal-taproot pyramidal neuron. Because of their prominent appearance in Golgi-stained sections and their trunk-like taproot, these were named ‘‘matriarch’’ neurons (referring to the matriarch’s prominent role in elephant society). They exhibited extensive dendritic branching, which suggests a broad sampling of cortical information. Impressive neurons for an impressive animal.