118 chp 5

why do we have brains

• To efficiently and effectively move through space

• This requires: integration of sensory input, organization of response output to those external stimuli, and modeling the world (predicting whats happening next)

what is the self control study and the results found from it

Procedure: Tested 36 species of mammals and birds using two tasks:

1. Food location: Animals had to find food after it was moved to a new location.

2. Transparent cylinder: Animals had to resist reaching directly for visible food and instead go around the barrier.

Findings: Species with larger absolute brain sizes generally showed better self-control, regardless of relative brain size or EQ

what 4 traits did the phylum chordata evolve

• Dorsal hollow nerve cord (CNS)

• Notochord (structural support and gets replaced by the vertebral column in vertebrates)

• Gill slits (breathing)

• Postnatal tail (swimming)

  • These are all adaptations for rapid sensory integration and movement

chordata evolved in water

what are features that evolved in the sub phylum vertebrata

• Vertebrate skeleton:

  • Backbone: encases the spinal cord

  • Internal skeleton: allowed for evolution of antagonistic muscle systems (gave way to fine tuned movement)

  • Cranium (skull): encases the brain

what are the vertebrate brain strucutres (3)

• Began as 3 bulges at the anterior end of spinal cord

  • Prosencephalon (forebrain)

  • mesencephalon (mid brain)

  • rhombencephalon (hind brain)

what structures make up the prosencephalon

• Telencephalon (olfactory bulb, cerebral hemispheres, limbic system, striatum)

• Diencephalon (thalamus, hypothalamus)

what structures make up the mesencephalon

Tectum and tegmentum

what structures make up the rhombencephalon

Cerebellum and brain stem (pons and medulla)

how does the evolution of the front end vs the back end of the nervous system compare to one another

Back end of the nervous system is more consistent across species whereas the anterior end is more variable (this is due to complexity of organism and the environment that shaped the species)

what is the evolution of spinal brain projections and the 4 different forms that took shape

• Sensory or afferent information comes into the spinal cord through the dorsal roots and efferent or motor information travels away from the spinal cord through ventral roots

• More direct connections between spinal cord and higher brain areas evolved as behaviors become more sophisticated, and required more direct communication between the brains “control centers” and the body

• Spinoreticular evolution is of the spinal cord and reticular formation which illustrates many of the innate behaviors occur in the spinal cord

• Spinocerebellar evolution is the spinal cord and cerebellum, the volution of jaws required more muscle coordination

• Spinothalamic evolution is the spinal cord and thalamus which evolved to allow for more sensory integration

• Palliospinal evolution is the spinal cord and the cerebral cortex which evolved as endotherms due to moving more and using more energy 

what is the evidence of learning in the spinal cord (simple learning, associaion learning, instrumental learning)

• There is also evidence of neural plasticity in the spinal cord.

• In the bullfrog repeated stimulation of axons in the lateral column of the spinal cord leads to a decreased response output through the ventral root (habituation)

Pavlovian learning in spinal rats

• Spinal cord is surgically disconnected from the brain spinal cord has to learn independently of the brain 

• During training the rats received a mild shock to the right leg, which preceded a fear inducing shock (CS+)

• The left leg received the same mild shock which preceded the absence of shock (CS-) 

• During test they applied heat to the tail after stimulation of either legs and measured how long it took them to remove their tail from the heat

• Found that after right mild shock they were able to leave the tail on the plate longer due to an analgesic response

  • The spinal cord predicts a strong shock, therefore  initiating an analgesic reaction which induces pain suppressing hormones in anticipation of the pain. 

Instrumental learning

• The rats would receive a shock every time they relaxed their leg and learned to keep their leg flexed to avoid shock

• Response outcome relationship is encoded here

where is the locus of eye blink conditioning and what is it

• Have a third eyelid that is a membrane that causes blinking

• Rabbits can associate  a tone with a puff of air and blink in order to predict the puff

• Locus of this condition happens in  the cerebellum (IN) will start firing once it hears the tone which precedes the blink by 45 ms

  • Lesion studies have proved this

what are coincidence detectors

Neurons where the CS and US converge are called coincidence detectors

what is the role of mesencephalon

• Mesencephalon consists mainly of the tectum (including the optic lobes), which contains nuclei that serve as centers for visual and auditory reflexes

• Mediates most complex behaviors of fished and amphibians, integrating visual, tactile, and auditory information

  • Toads tectum have cells that respond to smaller stimuli (food) compared to larger stimuli (possible predators) 

  • This visual detection combined with toads motivational state and experiences drive whether the toad will eat or protect itself 

  • This is possible because the tectum is retinotopically organized with the retina 

• Plays a large role in birds, too, but the cerebrum took over some of the midbrain functions

• In mammals the midbrain is mainly a relay center for information on its way to higher brain centers

what is the role of the diencephalon

• Subdivision of the prosencephalon (forebrain)

• Regulation of daily rhythms, thermoregulation, mating and migratory behaviors

  • These rhythms run through the pineal gland which converts serotonin to melatonin

what is the role of the hypothalamus (as well as its ability to learn) and the thalamus in the diencephalon

• Hypothalamus

  • Regulates endocrine system via the pituitary gland

    • Some neurons release oxytocin a vasopressin  to our bloodstream through the posterior pituitary gland

    • Other neurons release releasing factors to the anterior pituitary which release other hormones to act on other parts of the body 

    • maintains homeostasis

  • Biases associative learning toward reward predictive cues

    • he LH works with the BLA and VTA to guide learning toward reward-predicting cues, using dopamine signals to indicate when rewards are better or worse than expected.

  • Escape learning too 

• Thalamus

  • Is the origin of many of the brain waves that regulate functional organization across cortex, striatum, and limbic systems 

  • Basis of consciousness

    • Bc it is so integrated in so many cortical processes

what is the role of the subdivisions of the telencephalon

• Pallium

  • Hippocampus (spatial behavior, episodic memory)

    • Birds that store food have larger hippocampus 

    • Important for homing pigeons 

  • Cortex (higher - order perceptual processing, working memory, semantic memory)

• Subpallium

  • Amygdala (learning and emotional behavior)

    • Lesions impair fear conditioning

  • Basal ganglia (action selection, motor behavior, reward learning)

    • Damage to dopamine input is Parkinson's disease 

• These systems are deeply conserved across vertebrates

what is the emerging view of the brain as a prediction organ

• Emerging view of the brain as a prediction organ

  • Simulates the world

  • Makes predictions of future states following actions

  • Then validates predictions by gathering sensory input to compare to predictions

  • learning/memory is the process of updating the model of the world when predictions are not confirmed

    • Feedback loop

      

what is the encephalization quotient and biological intelligence

• EQ is the ratio of relative/expected brain size (determined by scaled body size)

• Biological intelligence: capacity to construct a perceptual world (modeling) 

• Essentially how far the species is from the line of expected brain and body size 

  • Above the line the eq is greater than one and larger than expected (encephalization)

what are examples of brain size increased more often than decreased

• Brain size increased independently in cartilaginous fishes, somme bony fished, birds, mammals

  • Early mammals were nocturnal and relied on other senses instead of vision (which are processed in the brain)

• Brain size decreased in salamanders, and eels

  • Brains are expensive to maintain

what is the comparative neuroanatomy (midbrain and forebrain))

• Scale size of brain areas relative to whole brain

• Relative volume of midbrain decreased and forebrain increased relative to rest of brain during vertebrate evolution

• Why has there been an increase in reliance on forebrain vertebrate, especially mammalian evolution? 

  • Increased behavioral flexibility 

• Body size got larger too

what is the learning of learning sets in mammals

• Stimulus discrimination task:

• Two stimuli are presented in the apparatus and subject has to choose between the two. One stimulus (S+) gives a food reward and the other (S-) does not give a food reward

• Experimenter will present stimuli over many trials until 80% success rate is observed. Then the experimenter will present a new set of two stimuli and continue this process over many trials and sets of stimuli. 

  • Win-stay / lose-shift: new items are presented and you will stay picking the item that produces a win and shift if your choice presents a loss. 

• Experimenter then discriminated learning through measuring the percentage of correct choices on trial 2 (this is because once you understand the rules of the game it only takes one trial to be successful going forward)

  • Evidence of learning is shown when your percentage correct on trial 2 is above 50 percent (chance)

    

what are the two methods to study flexible behavior

learning of learning sets, and reversal learning

what is discrimination reversal learning

• Correlated with degree of frontal lobe development in primates, that is these primates do better with reversal learning

• Transfer index=rate of reversal learning compared to original learning 

  • Positive = faster reversal learning

  • Negative = slower reversal learning

• Same apparatus except stimuli remain constant rather the reward associated with the stimuli gets reversed once they reach proficiency (80 percent).

• Lesions of the frontal cortex affect this test a lot (don't have impact on discrimination learning)

why are bigger brains better

• Smarter 

• More flexible behavior

• How does increased brain size produce increased intelligence?

  • Functional connectivity (neurons)

what are the two models for how neural networks change with size

• Bigger brains have more neurons

• Maintaining proportional connectivity

  • As number of neurons increase the number of axonal connections increases too

• Absolute number of connections maintained

  • As number of neurons increase the number of axonal connections stays the same

• There is more evidence for maintenance of absolute connectivity

• Thus, larger brains have more subdivision and are more sparsely connected and have distinct functionalization

  • Analogy of a growing company and development of departments

    

what are the two types of evolution of new brain structures and example of least common one

• Phylogenetic conversion: over evolutionary time (phylogenesis) over time the specific brain structure converted into a different type relative to the ancestral population

  • Mammalian neocortex: homologous to dorsal pallium of other vertebrates

  • Birds and other vertebrates = nuclei - ancestral condition

• Phylogenetic proliferation(Common): the change in the brain created two new subdivisions (new areas proliferate from the original

what are the two forms of phylogenetic proliferation and examples

• Phylogenetic addition: where the new structure is added additionally to the derived ancestral structure

• Phylogenetic segregation: each of the new subdivisions changes relative to the ancestral state

• Proliferation by phylogenetic segregation

  • None of the lemnothalamic nuclei in amniotes(lizards, birds, mammals) are homologous in a one to one manner to a single lemnothalamic nucleus in anamniotes(amphibians)

• Proliferation by phylogenetic addition

  • “Old” homologous neocortical structures in red (primary and secondary sensory and motor areas). “New” areas include higher order sensory or association cortices 

  • Larger brians have new higher order sensory cortices

what are the scaling rules of the cerebral cortex (dorsal pallium)

 rules for cerebral cortex (dorsal pallium)

• Nonprimate mammals: as number of neurons increases. Neuronal density decreases. That is as brain size increases, neurons ger larger and number of neurons per volume of brain tissue decreases.

• Primates: as primate cortex gains neurons, neuronal density stays the same. That is as brain size increases, number of neurons per volume of brain tissue remains relatively constant

  • Birds follow same scaling rule 

• Therefore as cortex size increases, the number of neurons in cortex increasesat a much higher rate in primates than in non primates.

• More neurons = more computing power

• Thus a primate and bird will have more computing power than a non primate mammal of the same sized cortex (dorsal pallium)

what are amniotes and anamniotes

Amniotes are vertebrates that develop an amniotic sac during embryonic development, including reptiles, birds, and mammals. Anamniotes, such as amphibians and fish, do not have this structure and typically lay eggs in water.

what are the 4 evolutionary concepts in neuroanatomy

• Parallelism: character similarity due to independent evolution from similar basal characters

• Convergence: independent origin of similar traits from distinct ancestral features

• Reversal: evolutionary return of a descendant trait to a remote ancestral state

• Divergence: phenotypic differentiation of homologous traits

what are the 5 criterior for establishing neural homology

• Topography: relative spatial position of the structure within the CNS

• Pathways: pattern of afferent and efferent neuronal connections

• Cytoarchitecture: cellular organization into layers, laminas, or nuclei

• Neurochemistry: specific neurotransmitter and neuromodulator profiles

• Gene expression: conservation of developmental gene or protein expression patterns

what are the two character stability: cranial nerves and neurochemical systems

• Cranial nerves: Cranial nerves are formed by axons carrying afferent information from the periphery into the CNS and by axons carrying efferent information from the CNS to the periphery (muscles, glands, organs, and sensory receptors).

• Also stable across species are the neurochemical systems: bundles of axons that connect different structures and use a specific neurotransmitter

  • Neuromodulators are substances that influence neurotransmitter receptors in the postsynaptic membrane or neurotransmitter release and reuptake in the presynaptic membrane.

what are mauthner cells in the spinal cord

Mauthner cells: a pair of a giant brainstem interneurons present in agnathans, teleosts, and amphibian larvae. Mauthner axons decussate and form fast electrical synapses with contralateral motor neurons, driving a rapid escape swim contraction away from predators

what is the role of the medulla, pons, cerebellum

The medulla, pons, and cerebellum are key brainstem structures that together coordinate vital functions. The medulla regulates autonomic functions like breathing and heart rate, the pons facilitates communication between different parts of the brain and controls sleep, while the cerebellum is involved in balance, coordination, and motor control.

What role does the telencephalon play in learning in goldfish?

Goldfish without a telencephalon can still learn basic associations and escape shocks but struggle with active avoidance. Stronger shocks improve their learning, suggesting the telencephalon helps regulate learning rather than directly store memories.

what is the principle of proper mass and mass action in terms of brain size

• Principle of Proper Mass: The size of a specific brain region positively correlates with how much information it handles. For instance, visually oriented diurnal primates devote large areas to vision, whereas bottom-feeding catfish have enlarged brainstem nuclei to process taste inputs from their vagal nerves.

• Principle of Mass Action: Proposed by Karl Lashley, this principle states that when brain functions are distributed across multiple areas, the severity of a learning deficit depends on the amount of tissue lost rather than where the damage occurs.

what is the example of artificial selection for brain size

• Kotrschal et al. selectively bred guppies for high vs. low relative brain size over two generations

• Cognitive Outcome: Large-brained females achieved significantly higher accuracy in a visual numerical discrimination task (4 dots vs. 2 dots) than small-brained females (no effect observed in males)

• Fitness Trade-off: Large-brained guppies suffered an energetic trade-off, producing significantly fewer offspring in their first brood compared to small-brained controls

what are the two main determinants of brain size

• Allometric change: Brain size increases as body size increases, partly through longer cell proliferation.

• Encephalization: Natural selection favors a larger brain beyond what body size predicts.