Hippocampal Circuit Diagram

[Caitlin Vander Weele]

Its too big for me to put on the google doc....

I think its correct but let me know if you find any mistakes.

Caitlin

[Rishi Rajalingham]

Only fix I would make to that is that they're called collaterals, not contralaterals (schaffer collateral, recurrent, etc..), and the step after orthogonalization is for pattern completion, not computation. 

Hope the studying's going well!

Caitlin

--
 
 

[Caitlin Vander Weele]

Thanks... had trouble deciphering my own handwriting...

--
 
 

--
Caitlin M. Vander Weele
Ph.D. Graduate Student
Brain and Cognitive Sciences
Massachusetts Institute of Technology
Phone: (989) 274-8757
E-mail: cai...@mit.edu

[Caitlin Vander Weele]

FIXED

[Hannah Frances Iaccarino]

hi!

question: doesn't CA1 send output to EC as well?

--
 
 
<Hippocampal Circuit2.jpg>

[Lea Hachigian]

yes to the deep layers

Sent from my iPhone

[Caitlin Vander Weele]

Great catch. Thanks!

Version 3 attached....

[Max Kleiman-Weiner]

Do you think it would be OK to print this out and turn it in as part of the exam?

--
 
 

[Hilary Richardson]

only if you include a cartoon of a person hand-waving/shrugging for the functional description.

--
 
 

[Hannah Frances Iaccarino]

or this…

On Dec 16, 2012, at 2:06 PM, Hilary Richardson <hlr...@MIT.EDU>

 wrote:

--
 
 

[Caitlin Vander Weele]

Too bad its not multiple choice.... http://whatshouldwecallgradschool.tumblr.com/post/38064654775/taking-a-test-i-didnt-study-for

[Hilary Richardson]

sorry, but do we know for sure that the medial septum projects to CA1? i know it projects to the hippocampus, but don't have it in my drawings, and wikipedia isn't helping... just checking. 

--
 
 

[Caitlin Vander Weele]

Something does... Its the septum right?

[Dheeraj Roy]

Yes. The MS sends inhibitory projections to CA1.

-DR

Sent from my iPad

On Dec 16, 2012, at 2:33 PM, Hilary Richardson <hlr...@mit.edu> wrote:

sorry, but do we know for sure that the medial septum projects to CA1? i know it projects to the hippocampus, but don't have it in my drawings, and wikipedia isn't helping... just checking. 

On Sun, Dec 16, 2012 at 2:18 PM, Caitlin Vander Weele <cai...@gmail.com> wrote:

Too bad its not multiple choice.... http://whatshouldwecallgradschool.tumblr.com/post/38064654775/taking-a-test-i-didnt-study-for

On Sun, Dec 16, 2012 at 2:12 PM, Hannah Frances Iaccarino <h...@mit.edu> wrote:

or this…

<direction_confusion1.jpg>

--
 
 

[Hilary Richardson]

thanks :) 

On Sun, Dec 16, 2012 at 2:37 PM, Hannah Frances Iaccarino <h...@mit.edu> wrote:

yeah it does, for sure. it has an inhibitory synapse onto an inhibitory neuron that synapses on CA1. so it activates CA1 through disinhibition.

i'm looking at the drawing from my notes that day.

On Dec 16, 2012, at 2:33 PM, Hilary Richardson <hlr...@MIT.EDU>

 wrote:

sorry, but do we know for sure that the medial septum projects to CA1? i know it projects to the hippocampus, but don't have it in my drawings, and wikipedia isn't helping... just checking. 

On Sun, Dec 16, 2012 at 2:18 PM, Caitlin Vander Weele <cai...@gmail.com> wrote:

Too bad its not multiple choice.... http://whatshouldwecallgradschool.tumblr.com/post/38064654775/taking-a-test-i-didnt-study-for

On Sun, Dec 16, 2012 at 2:12 PM, Hannah Frances Iaccarino <h...@mit.edu> wrote:

or this…

<direction_confusion1.jpg>

--
 
 

[Rishi Rajalingham]

Does anyone have a good intuitive sense about the origins of theta rhythms in CA1? 

The medial septum is usually thought to be the source of hippocampal theta (obviously this is difficult to prove). Would oscillations arise from feedback mechanisms involving septal input to EC or CA1? In the attached figure, it shows septal input directly to CA1 (for disinhibition), which could work (SM disinhibits CA1 which inhibits it after some time lag, resulting in oscillations), but nothing I've read so far suggests this. Instead, it seems like theta arises from the direct pathway from EC to CA1, and MS controls this via input to EC (so something like SM inhibits EC, which inhibits CA1, which releases it from inhibition, resulting in oscillations). Any ideas?

--
 
 

[Stephanie Tagliatela]

From my notes:

EC inputs to CA1 are rhythmically modulated.  Spiking activity of CA1 is phase locked to EC. theta activity is maintained by phase shifted feedback inhibition. GABA and ACh neurons are modulated by theta rhythm...

So we have neuromodulatory inhibition of excitation (modulated by theta) + rhythmic modulation of membrane potential and spikes via EC

This makes me think that theta rhythms in CA1 are derived from direct inputs from both EC and MS. According to the circuit diagram, MS provides direct ACh and GABA input to CA1.

Below is a more verbose version. Thoughts?


rhythmic modulation in terms of theta rhythm (10 Hz) observed in field potential: dipoles of currents are rhythmically syncrhonized, input property? yes, EC cortical inputs to CA1 are rhythmically modulated--> spiking activity is also modulated by theta (phase locked to EC: spiking is correlated with phase of extracellular rhythm)

Input to CA1 is phase locked--> oscilations in LFP, membrane potential does something similar: phase relationship between structures is not obvious: membrane potential might be phase shifted in some way. If membrane potential is oscillating, what would you expect spike production to look like?  At the peaks! Modulated along spatial AND temporal scale (peaks of oscillations)
So both spatial and temporal position modulate spiking probability

Input drive is also modulated as a function of position.

If you hit a cell with input, they tend to resonate at this frequency.  Also circuit mechanisms activated by it’s output: when an AP is produced, it creates inhibition. There is also inhibitory modulation that is roughly the same, but slightly phase shifted. So we have LTP, modulation of membrane potential, spatial modulation, and inhibitory regulation: through feedback mechanism, and control from basal forebrain strucutre (medial septum: provides source of ACh and GABAergic projections) Cholinergic terminate on pyramidal cell dendrites: GABA and Cholinergic neurons are modulated by theta rhythm.

So neuromodulatory inhiition of excitation, theta rhythmic input from EC, rhtymic modulation of membrane potential. This somehow creates place cell coding...

--