Week 7 (March 13 & 25): Dynamics in neural microcircuits
Chris Harvey (harvey@hms.harvard.edu)
In March 13’s lecture, we will discuss the fundamentals of activity dynamics in neuronal circuits.
In a dynamical systems framework, we will examine the principles by which activity in circuits
changes over time to carry out computations. The goal of the lecture is to emphasize how
measurements of circuit dynamics can provide a mechanistic understanding of circuit function.
We will also discuss how dynamics complement and expand on studies of neural coding in
systems neuroscience. We will examine three types of dynamics in detail: attractor dynamics
using short-term memory as an example, oscillations in the context of central pattern generators,
and sequences of activity during motor actions.
On March 25 we will discuss:
 Long, M.A. and Fee, M.S. Using temperature to analyse temporal dynamics in the
songbird motor pathway. Nature 456:189-194 (2008).
Your assignment is to design experiments based on the questions listed below, which follow
from the discussion paper. Please pay attention to the guidelines and suggested format. The
length of the answer to each question can be as long or short as needed, but approximately 0.5
pages per answer is a target length.
If the goals of the assignment are not clear or if you wish to discuss the assignment, please
contact me by email or stop by my office (Armenise 417).
The goal of this homework is to think about the design of experiments to test specific
hypotheses. Here we are focused on testing the models raised in Long and Fee 2008 and also on
testing which circuits establish the dynamics for behavioral outputs.
Your answers will be judged on how well your proposed experiments test the predictions of the
hypothesis, the feasibility of the proposed experiments, and the thoroughness of your
experimental design (are all key parts of the proposed experiment considered and described?).
For each set of proposed experiments, please:
- State the specific prediction of the hypothesis you are testing
- Explain the key methodological and experimental details you propose
- Explain the analysis methods you will use to analyze the data, where applicable
- Include a discussion of the predicted experimental results
- Include an interpretation of what the possible experimental outcomes will mean in
terms of accepting or rejecting the hypothesis
Questions:
1. The authors discuss the inter-hemispheric synchronization of signals in HVC (see
Supplementary Fig. 11, page 193, Supplementary Discussion VII-VII). They propose a model in
which “HVC is broken up into multiple syllable-length chains (or modules), each of which can
run autonomously by virtue of circuit dynamics within HVC. These modules may then be linked
together in time by the feedback connections from RA through thalamus and back to HVC. The
feedback circuitry may act to detect the end of one syllable and rapidly and bilaterally initiate the
next module, thus simultaneously continuing the song sequence and re-synchronizing the two
HVCs.”
Propose experiments to test a specific aspect of the model that feedback circuitry from RA
through thalamus back to HVC contains a synchronization signal that bilaterally synchronizes
the start of activity in HVC at the beginning of each syllable. These experiments should focus on
ways to test if such a synchronization signal exists in the proposed RA-thalamus-HVC pathway.
As a starting point, consider the key features that such a signal would exhibit.
2. A major claim of Long and Fee 2008 is that the dynamics for song production are set in HVC.
Also, previous experiments have shown that HVC neurons fire sequentially (one neuron after
another) in temporally precise bursts (see Hahnloser et al Nature 2002). This has led the authors
to propose that HVC neurons form domino-like chains of activity that run autonomously to
control the timing of the song.
If you are convinced by the data supporting this claim, then propose experiments to test the
synaptic connectivity and circuit architectures underlying the “domino-like chains”. How could a
circuit be organized to mediate this type of activity and what experiments can be done to test this
organization? Proposing and testing one hypothesis of circuit organization is sufficient.
If you are not convinced by the data supporting this claim, then propose additional experiments
to test specifically the model of an autonomously running domino-like chain in HVC. What are
specific predictions of the domino-like chain model and how can one specific prediction be
tested experimentally?
3. A graduate student is using a new model system for systems neuroscience, the Etruscan tree
shrew, to study motor control. She has found a new rhythmic, oscillatory motor movement (at
~10 Hz) that the tree shrew uses during prey capture. Based on comparisons to other systems,
she hypothesizes that the circuits controlling the timing and generation of the oscillatory motor
behavior are located somewhere in the shrew’s brain, not in the spinal cord or brain stem.
Outline an approach to localize candidate brain areas for controlling the generation of the timing
of this oscillatory behavior. This outline should illustrate a systematic approach to localize
candidate areas but need not include as extensive an experimental description as in Questions 12. Your design should start with a description of the key features this area is likely to possess and
how you will design an approach to find those features. Finally, include a brief description of
how you could demonstrate if any of the identified candidates causally determine the timing of
the oscillatory motor action. The outline of the approach should include experiments that could
perhaps be accomplished in the time of the student’s PhD thesis.