Introduction To Behavioral Neuroscience Exam #2 University of Iowa

Evolution (6-1)

Refers to a gradual changing of one species into another.

Evolution is ... (6-1)

indifferent - change occurs over time regardless if it is helpful or harmful to the species.

"Scale of Nature" (6-1)

For centuries, we have made attempts to classify and order things in nature into categories and groups.

Carl Linnaeus (6-1)

Published Systema Naturae classification of animals based on similarities (1730's).

Pre-Darwinian Ideas on the Origin of Species (6-1)

It was thought that each species was created separately before the 1800's (e.g. if species had been created specifically for different types of locomotion, then they should have been built on a different plan).

Then naturalists began to have doubts: they noticed that limb bones from all mammals were similar (regardless of their way of life).

Also, 19th century geologists were discovering that the earth had been changing for millions of years (newly discovered fossils provided additional evidence for evolution).

Paleontology (6-1)

Branch of science concerned with fossils of animals and plants.

Darwin's Theory (6-1)

Based on many years of research (esp. in Galapagos Islands). Darwin published On the Origin of Species by Means of Natural Selection (1859).

Alfred Russell Wallace (6-1)

Conducted key observational work in Indonesia that contributed to Darwin's theory (but he later drifted into obscurity for several reasons).

The Four Observational Bases of Darwin's Theory (6-1)

1) Reproduction increases population size unless factors limit it.

2) Individuals in a species are not identical .

3) Some variation among individuals is due to inheritance.

4) Not all offspring survive to reproduce.

Darwin's Conclusion (6-1)

Variation among individuals affects the probability of surviving & reproducing, and therefore passing on those characteristics.

Natural Selection (6-1)

Process whereby traits become more or less common based upon differential reproduction over time.

Adaptations (6-1)

Traits which increase the probability of survival of the organism.

Fitness (6-1)

How well a species or member of the species "fits" into its niche.

Analogy (6-1)

Similar function; doesn't necessarily indicate any evolutionary connection (be careful to NOT mix up this with h**ology).

Homoplasy (6-1)

Similar features that evolved separately (e.g. bats and birds, dolphins and fish).

Highlights the idea that species may independently evolve similar traits as a result of having to adapt to similar environments.

Homology (6-1)

Features based on common ancestry.

The Gap in Darwin's Theory (6-1)

The inability to isolate the source of variation by natural selection or the mechanism of inheritance.

Mechanism of Inheritance (6-1)

Genes for inherited traits are encoded in DNA inside all cells.

Started with Gregor Mendel's (1879) laws of inheritance and later culminated in Watson and Crick (1950) solving of the 3D structure of DNA.

Source of Heritability (6-1)

Genes are present across all species (23 chromosome pairs in humans).

Some genes are highly conserved.

Others genes are very different (or non-existent) from one species to the next.

Considerable genetic similarities are present among all organisms.

Highly "Conserved" (6-1)

Remain unchanged across species.

Natural Selection at the Genetic Level (6-1)

Mutations create variation.

Unfavorable mutations hamper reproduction and are selected out.

Reproduction and mutation continue.

Adaptive mutations are favored (and spread throughout the population).

Classification Now (6-1)

With Darwin's theory and Linnaeus's classification scheme: NOW requires a common ancestor (species -> genus -> family -> order -> class -> phylum -> kingdom [most specific -> broadest]).

Today we classify species based on phylogenetic closeness (with the help of modern genetics).

Taxonomy (6-1)

Classification system of organisms.

Phylogeny (6-1)

Evolutionary history of species.

Genes and Mutations (6-1)

Changes in DNA can serve as a "clock": AKA the rate of DNA change is constant.

Most changes in DNA do not affect genes. Some may be adaptive or maladaptive (remember, the process of evolution is indifferent/random).

So we can use changes in DNA to estimate when two species diverged from a common ancestor.

Key Points: Evolution (6-1)

1) Is NOT linear or goal-oriented.

2) Successful characteristics depend on selective pressures on species which change over time.

3) Referring to species "primitive" and "advanced" is a misnomer- ALL species are evolving to ensure good "fitness" in their niche.

4) Takes hundreds of thousands - millions of years.

Selective Pressures (6-1)

Aka environment.

Why Should We Study a Particular Species? (6-1)

Outstanding features.

Convenience.

Comparison.

Preservation (usually done in the field).

Economic importance.

Treatment of disease.

More ethical than human trials.

Drosophila Melanogaster (6-1)

Aka the fruit fly.

Easy to perform genetic analyses on.

Short generational cycle (few days).

Simple nervous system.

Small, cheap, easy to house.

Few ethical concerns.

C. Elegans (6-1)

Aka nematode worm.

Easy to perform genetic analyses on.

Short generational cycle.

Even simpler nervous system than fruit fly (302 neurons).

Small, cheap, easy to house.

Few ethical concerns.

Aplysia californicus (6-1)

Aka sea hare.

Simple nervous system (~15,000 neurons).

Neurons are large and easy to identify.

Few ethical concerns.

Rodent (6-1)

Better model for comparison to humans (i.e., vertebrate and mammalian).

Easy for genetic analyses (esp. mice).

Relatively inexpensive to house/breed.

Larger nervous system -> easier for neuroscience experiments (esp. rats).

Significant ethical concerns.

Warbler Species (6-1)

Size of brain region (HVC) correlates with the number of songs that this species can produce.

Brain Evolution (6-1)

The amount of brain devoted to a structure relates to the importance of that function subserved by it (e.g. food storing and hippocampal size have a positive correlation in birds that store food).

Basic Similarities in NS Across ALL Vertebrates (6-1)

Development from a hollow dorsal neural tube.

Bilateral symmetry.

Segmentation.

Hierarchical control.

Separate systems.

Localization of functions.

Brain Structure (7-1)

Brain parts are basically the same, but with some changes in regions/ functions as complexity increases.

Some Regions' Functions Have Changed/Been Altered: (7-1)

E.g. midbrain optic tectum responsible for visual processing in lower vertebrates - has become visual reflex center in mammals whereas occipital cortex is more important for visual processing.

Mammals (7-1)

All ***** have a mix of allo- and neocortex (i.e., 4 vs. 6 layers).

More Recent Mammals (7-1)

Greater amount of real estate (>50%) devoted to neocortex.

Reptiles (7-1)

Have 3-layered cortex (may be more homologous to mammalian hippocampus, which also has 3 layers).

Brain-Body Ratio (7-1)

Some small mammals have greater brain-body ratio than humans.

Encephalization Factor (7-1)

Takes into account each class's deviation from the slope of the ratio of brain weight: body wt. for all species.

Cortex Size Increases With: (7-1)

Brain size (and not other regions).

Expansion of ***** Occurs In More Recent Ev. (7-1)

Cortex & Neuron Complexity.

Development (7-1)

Generally, regions of the brain that develop later during gestation/ development become larger (suggesting that small changes in genes involved in later brain development can translate to big changes in the brain).

Order of Bipedal Species Ev. (7-1)

Ardipithecus ---> Australiopithecus ---> Homo Habilis, Homo Erectus, Homo Sapiens (HH & HS overlap with HE, but not eachother)

Cerebral Volume (7-1)

Has increased significantly over bipedal species in the last 1.5 mil years.

Australopithecus (7-1)

First appeared ~4 mil yrs ago.

Bipedal (upright) hominids.

350-400 cm3 cerebral volume (size of chimp).

Made and used crude stone tools (chimps use, but do not make, tools).

Tool-making ability likely reduced selective pressure for large jaws and teeth (may also relate to increasing social tolerance).

Homo species (7-1)

Within last 2 mil yrs (and brain volume seems to have reached a plateau during this time).

Homo Habilis (7-1)

Cerebral volume of 600-700 cm3.

Homo Erectus (7-1)

Cerebral volume of 700-1400 cm3 (i.e., it expanded over a 1.5 million-year period).

Made elaborate stone tools, used fire, and killed large animals. Spread over three continents (i.e., from Africa Asia, Europe).

Homo Sapiens (7-1)

Emerged ~150,000 yrs ago - 1400 cm3 cerebral volume.

Migration of Homo Sapiens (7-1)

Recent radiocarbon dating shows that colonization is more recent than previously believed.

East Africa ~70,000 years ago, then West Asia ~47,500 years ago, across Berling Strait ~17,500 years ago.

Down Sides of a "Big Brain" (7-1)

Long gestation.

Burden on mother and childbirth.

Birth is difficult due to the large size of the baby's head.

Much growth and brain development occurs following birth.

Require prolonged dependence and parental care.

Although brain makes up only 2% of body weight, it uses majority of metabolic energy at rest.

Complex genetics required in development; prone to errors leading to behavioral disorders (e.g., schizophrenia, autism).

Why's the Human Brain so Big? (7-1)

Rapid expansion in brain size should be indicative of a strong advantage for survival.

What selection pressures favored this change?

There are some theories (social brain, sexual selection, behavioral innovations, tool use, and social learning).

Really: multiple sources of pressure were likely to have favored bigger brains in hominid brain evolution.

Social Brain Hypothesis (7-1)

Larger cortex is favored for handling the cognitively complex task of maintaining social relationships (Dunbar, 1998).

Sexual Selection Hypothesis (7-1)

Proposes a natural selection for abilities to attract attention, stimulate, and surprise a potential mate; also provides an evolutionary basis for understanding human traits of humor, art, language, and creativity.

Primate Species Differ in Gene Expression (7-1)

Humans and chimps have ~95% similar DNA, so we account for vast differences in brain and cognitive features by:

1) Genes specific to brain development (e.g., the ASPM gene is very different between these species, and deficiencies in humans leads to severe disability and small brain size)

2) Different expression patterns of genes in the brain (e.g. compare mRNA similarity in different organs between chimps and humans).

Chimps/Humans/Rhesus Monkeys (7-1)

Gene expression patterns (mRNA) differ more in brain than other tissues (like liver/blood differences which are pretty similar for H&C but are VERY different between H&C in brain).

Two Categories of Development (7-2)

Intrinsic (genetic) and extrinsic (environmental) factors.

Genotype (7-2)

Genes for traits contained within an individual.

Phenotype (7-2)

Physical characteristics (results from interaction of genotype with environment/ experience ).

Pre-Neural Dev. (7-2)

Initial development in zygote and embryo.

Then the fertilized egg (zygote) develops three layers: Ectoderm, Mesoderm, and Endoderm

[EXTRA Mesoderm - muscle, heart, red blood cells & Endoderm - lung, endocrine glands, pancreas]

Ectoderm (7-2)

Outer layer that forms during gastrulation that becomes the NS.

Transcription Factors [TFs] (7-2)

Earliest events in development are orchestrated by *****.

Orchestrate cascades of gene expression that allow for segmentation (body plan) and creation of specific tissue systems and cell types.

Since they are early are therefore common to all vertebrates

Transcription Factors are [highly or hardley] "conserved"? (7-2)

HIGHLY CONSERVED; TF that guide early developmental events are some of the most highly conserved genes in nature.

Body Plan Segmentation (7-2)

Set up from the earliest stages of embryonic development, and is highly conserved across most animals and all vertebrates (AKA huge overlap between species).

Homeotic Proteins (7-2)

TFs involved in body plan determination (segmentation); are highly conserved across evolution (e.g. "94.6% protein sequence homology, although mice and humans diverged 91 mil years ago!").

Gastrulation (7-2)

Developmental stage (when the embryo is approximately 2 weeks old) in which the human CNS begins to form:

1) Dorsal surface thickens forming a neural tube surrounding a fluid filled cavity.

2) Anterior end enlarges and differentiates into the hindbrain, midbrain and forebrain.

3) The rest of the neural tube becomes the spinal cord.

Stages in Neural Development (7-2)

**stages can overlap across-and-within regions**

1) Neurogenesis

2) Cell migration

3) Differentiation

4) Synaptogenesis

5) Neuronal cell death

6) Synaptic rearrangement.

Neurogenesis (7-2)

Cells on VZ undergo massive cell division (necessary source of neurons/glial cells).

Vertebrates are born with the most neurons they will ever have.

The increase in brain size thereafter is largely NOT due to an increase in the number of neurons.

Increase in brain size after vertebrate birth is accounted for by? (7-2)

Cell growth, increases in processes, glial cell production, and myelination.

What are the exceptions to post-natal neuron growth? (7-2)

To a limited capacity, well into adulthood, the olfactory bulb & granule neurons in the dentate gyrus (of the hippocampus).

Ventricular Zone [VZ] (7-2)

Inner side of neural tube (cells in the VZ provide the source from which all neurons and glial cells are derived).

What determines which kind of a cell is "born"? (7-2)

A combination of genetic and extracellular signals (e.g. TFs).

Cell "Birth Date" (7-2)

Since most adult neurons don't undergo cell division, the point at which they stop dividing is regarded as their *****.

Cell Migration (7-2)

The movement of the newly formed neurons and glia to their eventual locations.

Cortical migration occurs on "scaffolding cells" from the ventricular zone toward the outer (pial) surface (e.g. pyramidal neurons).

In the primate brain, all neuronal cell migration is complete by birth.

Radial Glia (7-2)

Aka scaffolding cells.

Tangential Migration (7-2)

Involves the movement of cells in the rostral-caudal axis (e.g. cortical interneurons).

Cell Differentiation (7-2)

Process of cells adopting their phenotype appropriate for the particular brain region.

During neuronal differentiation, axons grows first either during migration or once it has reached its target and is followed by the development of the dendrites.

Neural cell adhesion molecules [NCAMs] (7-2)

Class of chemicals expressed on the extracellular surface that GUIDE CELLS and growing axons to their appropriate targets.

Growth Cones (7-2)

Tips of growing axons; they contain filopodia at their tips.

Filopodia (7-2)

"Finger-like extensions" that detect chemicals in the local environment as they navigate.

Chemoattractants (7-2)

Class of signaling molecules, chemical signals that attract growth cones to enable guidance to their appropriate target neuron.

Chemorepellents (7-2)

Class of signaling molecules, chemical signals that repel growth cones to enable guidance to their appropriate target neuron.

Synaptogenesis (7-2)

The formation of the synaptic connections between neurons.

Occurs during brain development and widely throughout life as neurons are constantly forming new connections and discarding old ones.

Synaptogenesis slows significantly in later years.

Neuronal cell death occurs ***** during development? (7-2)

Throughout the NS.

Apoptosis (7-2)

"Programmed" mechanism (gene expression-dependent) for implementing cell death during development.

Necrosis (7-2)

The term used to describe cell death from injury or damage; usually occurs from trauma and/or disease.

Postsynaptic targets provide ***** to extending axons (7-2)

Neurotrophins.

Neurotrophins (7-2)

Allow for matching between size of target and the number of neurons with efferents to the target region (includes NGF and BDNF).

Necessary for presynaptic cells to survive (if deprived ---> they die)? (7-2)

Neurotrophins.

Nerve Growth Factor (NGF) (7-2)

Neurotrophin secreted in target organs (e.g., muscle) in the PNS.

Brain-Derived Neurotrophic Factor (7-2)

A key neurotrophin secreted by target neurons in the neocortex and hippocampus.

Synaptic Rearrangement (7-2)

The process whereby earlier formed synapses may be eliminated, while others are added.

More synapses: good or bad? (7-2)

It is likely the refinement (both formation and elimination), and not overall increase/ decrease in synapses that are important for memory storage.

Gliogenesis (7-2)

Development of glial cells [astrocytes, oligodendrocytes, Schwann cells, microglia] throughout prenatal development concurrent with neurogenesis; increases after birth in many animals, continues throughout life.

Myelination (7-2)

Occurs primarily after birth (for role of glia in brain development), in frontal lobe can last until 23-30 and even longer (esp. in males).

Glia in Brain Development (7-2)

Important for increasing AP conduction velocity ---> facilitates coordinated control of movements (later on: for better cognitive functioning).

Diffusion MRI (7-2)

To study myelination by mapping the diffusion of water in biological tissues ---> thus revealing fatty membranes of myelin.