Notes

Absolute and Relative Differences

Brain Mass versus Body Mass

Encephalization Quotient (EQ)

It describes brain size as a ratio of the expected average brain size relative to the actual body weight. Some scientists argue that EQ correlates with the intelligence of a species. Einstein:

• Average (or even smaller) total brain size
• Smaller neuron/glia ratio than average.

"Our results also suggest that Einstein had relatively expanded prefrontal cortices, which may have provided underpinnings for some of his extraordinary cognitive abilities, including his productive use of thought experiments. From an evolutionary perspective, the specific parts of Einstein's prefrontal cortex that appear to be differentially expanded are of interest because recent findings indicate that these same areas increased differentially in size and became neurologically reorganized at microanatomical levels during hominin evolution in association with the emergence of higher cognitive abilities.

Brain Evolution in View of Cortical Expansion

Cortical expansion is often equated with"brain evolution", whereby the relative size of the cerebral cortex increases while the relative size of the cerebellum remains fairly constant. Human cortical expansion is relative but does not affect each region similarly!

Cortical Expansion of Associative Areas

Prefrontal Cortex: Human vs. Rats Human Prefrontal cortex functions: Planning, Attention, Working Memory, Cognitive Flexibility and Impulsivity. Do rats have similar prefrontal structures and functions?

Assessment of Human prefrontal Cortical Functions

Example: Working Memory

• Short-term memory buffer with limited temporal capacity.
• Used to hold relevant information "online" in order to guide ongoing behavior, including strategic planning and problem solving.

Cognitive tasks which demand working memory activate the PFC: an fMRI investigation in humans

Assessment of Rat Prefrontal Cortical Functions

Effects of prefrontal cortex lesion on working memory in the 8-arm radial arm maze. Lesions to the medial part of the prefrontal cortex (mPFC) lead to working memory impairments as evident by the increased number of working memory errors in the 8-arm radial arm maze.

Prefrontal Cortex: Human vs. Rats The rodent prefrontal cortex (PFC) is not as anatomically complex as the primate; however, many of the critical neuroantomical and functional characteristics are preserved in rodents, which allow meaningful cross species comparisons relevant to study of the neurocognitive and neurobiological mechanisms that underlie changes in executive functioning across the lifespan. As indicated in the figure, the medial portion of rodent PFC (which includes anterior cingulate (aCg), prelimbic (PL), and infralimbic (IL) cortices) shares strong anatomical homology with primate dorsolateral PFC.

Cross-Species Comparison of Subcortical Areas

Cross-Species Comparison of Hippocampal Anatomy Schematic illustrations of the orientation of the hippocampal long axis in rats, macaque monkeys and human. The longitudinal axis is described as ventrodorsal in rodents and as anteroposterior in primates. Note that a 90° rotation is required for the rat hippocampus to have the same orientation as that of primates.

Cross-Species Comparison of Hippocampal Functions "Recalling Routes around London: Activation of the Right Hippocampus in Taxi Drivers" Positron Emission Tomography (PET) was used to examine the neural substrates of spatial memory retrieval in licensed London taxi drivers while they recalled complex routes around the city.

Activity in the human brain related to spatial navigation. (a) A virtual town was shown on a computer monitor, and subjects in a PET imaging machine used buttons to navigate the virtual environment. (b) Increased brain activity associated with spatial navigation was observed in the right hippocampus (purple) and left tail of the caudate (green).

Effects of hippocampal lesions on reference learning and memory in the Morris water maze: deficits in the acquisition of spatial reference memory parallel the magnitude of dorsal hippocampal lesions, but is hardly present following ventral hippocampal lesions.

Cross-Species Comparison of Amygdalar Anatomy Primary amygdalar nuclei and basic circuit connections and function are conserved across species. An enlarged image of the basolateral complex of the amygdala (BLA) and central nucleus of the amygdala (CeA) or analogues are shown next to a coronal section from the brains of a lizard, rat, cat, monkey and human. In Post-Traumatic Stress Disorders (PTSD), the amygdala is hyperactive in response to negative (aversive) emotional stimuli vs. neutral and positive stimuli.

Experimental investigations of amygdalar functions in rodents.

Classical Fear Conditioning: Effects of complete electrolytic lesions of the amygdala.

Cross-Species Comparison of Basal Ganglia Anatomy