1. “Levels of Analysis in Behavioral Neuroscience”
Ethan Gahtan
Associate Professor of Psychology
Adjunct Professor of Biology
Humboldt State University
BSS room 122

2. Outline My research on sensorimotor circuits in zebrafish larvae
Levels of analysis in behavioral neuroscience
Focus on circuit level and connectomes… worth the effort?
Take home messages

3. About Ethan Gahtan
Education
University of Minnesota, PhD Cognitive and Biological Psychology
Research- neural mechanisms of adaptive behavior
MA : Common reward systems in drug addiction
PhD: Brain inflammation as a cause of cognitive deficits in AD
Post doc and current: hindbrain circuits mediating sensorimotor behavior
Teaching
Behavioral neuroscience I (Fall) and II (Spring, with lab)
Evolutionary psychology
Psychopharmacology
Cellular neuroscience
Social Neuroscience

4. ON SABBATICAL!

5. Current research: Topographical mapping in sensorimotor circuits
The point of this example:
The topography of the retina must be mapped onto motor systems
Raises the question:
How do neural circuits do this?

6. Somatotopic maps in human cortex
Primary sensory cortex Primary motor cortex
Ascending from body Descending to muscles

7. Descending sensorimotor pathways in human and fish brain

8. –EO Wilson / Krogh’s Principle
“For every problem in biology, there exists a species ideal for its solution.”
–EO Wilson / Krogh’s Principle
Zebrafish larvae have good characteristics for a model species:
Homology Are vertebrates
Genetically tractable Forward/reverse genetics
Accessibility Transparent
Rapid development Autonomous hunters by day 5
Simplicity relatively few cells overall
Manipulation genetic, surgical, optical, environmental, etc etc
Morally permissive fish, but still vertebrates
Cost and ease of use unsurpassed for vertebrates

9. Individually identifiable neurons.
Zebrafish in behavioral neuroscience research
Individually identifiable neurons.
The ‘same’ neuron can be identified across animals
The only vertebrate where entire neural systems are composed of identifiable neurons!

10. Reticulospinal (RS) neurons – a focus of my research.
RS neurons form the main pathway from brain to spinal cord.
Information flow in sensorimotor circuits:
Sensory neurons 
RS neurons 
Spinal cord neurons
Many neurons in these pathways are individually identifiable in zebrafish
Identifiable neurons means synaptic connections can be mapped with cellular level precision
Question:
Are RS neurons somatotopically organized?

11. Strategy for identifying synapses onto RS neurons:
Anatomical tracing Targeted stimulation

12. “Levels of Analysis in Behavioral Neuroscience”
But first, what exactly is behavioral neuroscience?

13. Behavior
Biology
Observe /
manipulate

14. First, think of a behavior or mental state.
Levels of analysis in behavioral neuroscience.
Most behaviors can usually be studied at multiple levels. Which is the right one?
Common levels of analysis for human behavior (and mental states) include :
Deep
Superficial
Nucleotides
Genes
Molecules
Cells
Circuits
Neural systems
Organs
Organ systems
Development
Social environments
Physical environments
Evolutionary selection
First, think of a behavior or mental state.
Which level offers the best explanations for that behavior?

15. Contrasting popular levels of analysis in behavioral neuroscience
Behavioral pharmacology studies bet on an intermediate level of analysis
fMRI studies bet on a superficial level of analysis
Whole genome association studies bet on a deep level of analysis

16. Where does ‘computational neuroscience’ fit in?
Nucleotides
Genes
Molecules
Cells
Circuits
Neural systems
Organs
Organ systems
Development
Social environments
Physical environments
Evolutionary selection
“Molecular neuroscience” implies a molecular level of analysis of neuroscientific phenomena.
“Cellular neuroscience” implies a cellular level of analysis of neuroscientific phenomena.
Does “Computational Neuroscience” imply a particular level of analysis?

17. What’s missing in this level of analysis?
Case study: Depression studied at a very superficial (social environment) level of analysis
What’s missing in this level of analysis?

18. What’s missing in this level of analysis?
Case study: Depression studied at a very deep (SNP) level of analysis
What’s missing in this level of analysis?

19. Good hypotheses should make sense across different levels of analysis
Behavioral neuroscientists tend to work at specifics levels of analysis.
But if hypotheses at one level are correct, they should be consistent with facts at other levels.
Computational models are used at different levels to support or test hypotheses
Good hypotheses should make sense across different levels of analysis

20. Personal reflection on the “circuit” level… is it useful?
Assumption: Adaptive behavior can be explained in part
by the physical structure of neural circuits
Challenges: neural circuits are hard to access for study
neural circuit structure is hard to manipulate
Nucleotides
Genes
Molecules
Cells
Circuits ?
Neural systems
Organs
Organ systems
Social environments
Physical environments
Evolutionary selection
Rybak I A et al. J Physiol 2006;577:

21. The new face of circuit level analysis in behavioral neuroscience: CONNECTOMES

23. Circuit level analyses- Successes…
Monosynaptic stretch reflex
Central pattern generators controlling motor rhythms (spinal, pyloric)
Reversed OKR in Belladonna zebrafish mutant
Autosomal Dominant Compelling Helioophthalmic Outburst Syndrome (ACHOO Syndrome)
and limits… There are many ‘degrees of freedom’ of neural function, so structural can’t explain everything!
Excitation / inhibition
Neurochemical Modulation
Gene regulation
Plasticity
Developmental effects
Redundancy, etc etc
These influence circuit function without changing circuit structure. Yet many neural circuit models don’t incorporate them.
Bottom line: to understand how brains works, knowledge of neural circuit structure is necessary but usually not sufficient

24. Current Biology 2000, 10:595–598

26. THANK YOU! Take home messages
My research examines the synaptic structure of topographical maps in hindbrain circuits.
I teach courses in neuroscience, evolutionary psychology, psychopharmacology, and related
Good neuroscience requires a multiple levels of analysis approach (consilience)
The ‘right’ level to study depends on your goals, theory, and personal preference
The neural circuit level of analysis is necessary but not sufficient for understanding how brains work
me if you’re interested in talking more about this
THANK YOU!