Neurons are cells
The have all the normal fixins of cells: organelles, cytoskeleton, DNA, etc. But they are also unique in
various ways - dendrites (receive input from other neurons), axons (propagate information as electric
signal), synapses (electrical
Based on the information provided below as well as the information that we have
discussed in the lectures and the conferences, your job is to form a reasonable
argument for one of the three hypotheses for the origin of a recently discovered
Evolution: change in inherited characteristics of populations over generations.
Wallace and Darwin developed the theory of natural selection, starting from the basic idea that there
is phenotypic variation, and it is heritable (observation). This was inte
Whose bains can we compare? The level of resolution of phylogenies affects the resolution of the
comparison, so what levels do we compare these at?
Molecules: e.g. neurotransmitters are highly conserved, but there are changes in the area
Encephalization: evolutionary changes in brains towards either enlarged association area, or
We assume that big brains are good, but encephalization is not a rule of evolutionary progress
Enlarged association size - cerebral size increase.
Measuring encephalization: absolute mass/volume of endocranium, brain, brain parts. assuming
volume to neuron ratio is 1:1.
Allometrically corrected mass or volume measurements
- Calculate residual relative to log regression (brain:body, or cortex:rest of
Stephen Jay Gould + Lewontin criticized the adaptationist programme that said that every trait is an
adaptation, leading to just-so theories of adaptation. They argued that not every trait is an
adaptation, metaphorically comparing it to the spandrels of
Engineering-wise, a sheer increase in size has to be accompanied by other changes, or else it
would be really inefficient. Do subdivisions stay the same, but larger? Do they get further
subdivided? What does this mean for homology?
Connectivity: we spent a lot of time looking at grey matter area, brain size, structure
size, cell bodies. But a lot of species differences in behaviour are probably mostly due to
Deacons rule: large = well connected. For example, if we star
Mischel marshmallow tests in children - delayed gratification, impulsiveness vs.
- Go/nogo experiments in adults - refrain from hitting a button in response to
stimulus - assay prefrontal cortex. The Stroop effect: reading the
Revisiting the delay in experiments (Goldman-Rakic, Funahashi et al 1993)
Activity increases for stimulus that appears on the right, no matter if its a congruent or
incongruent instruction - as opposed to activity that predicts the motor response itself.
Mahlon DeLong: activity of a pallidum neuron oscillates with oscillating motor
Brotchie et al 1991: wrist movement task: activity peaks after a new instruction,
and spikes again before a predicted movement.
Hikosaka 1998: cells activate stronger
Comparing basal ganglia across species: highly conserved. All tetrapods have a dorsal and ventral
striatum, and dorsal and ventral pallidum
Other anamniotes, e.g. lampreys: known to have a striatum, found to have a pallidum, subthalamic
nucleus (STN). The