MAYFORD Mark Scripps Genetic Control of MEMORY 28 Feb 2013

SINTN Lecture at Stanford in Clark Aud: 4:30P Thursday

activity induced genes

IEG transcription = immediate early genes

all this resch was done in mice.

use cfos-P  promoter   (trying to find and test " Halle Berry neurons"  ie  grandmother neurons)

Tet  based active circuit tagging...

tetracycline

tagging window:

when mouse is reared, it is continually fed doxycycline which blocks
transcription of a particular protein;

then during the tagging window,  take  doxy out of food of mouse...

Some questions that he would like to answer:

do the same neurons that are activated during learning become reactivated during recall???

does the strength of the memory depend on the strength of circuit reactivation

is there memory relevant offline activity in the neurons (after training but before recall eg)   etc.

******

Fear conditioning... paradigm - Pavlovian cond.

learning  tone-shock pairing in mice

shock animal: foot shock from a gridded floor... tone, shock  tone shock; do tone/ shock pairings.

context is an explicit form of memory and is  HC = hippocampus dependent form of memory

cued (eg with tone) is implicit and does not dep on HC...  play tone and mouse will be fearful and will freeze.

both forms of learning are dependent on the amygdala
.
keep animals on doxy until the actual training episode;

then keep animals OFF doxy and wash it out...

then neural firing will  activate  fos  etc..

and will activate our fancy marker  LAC

shock leads to => freezing...

what happens to  tag that is activated during learning...

compare: 

HC = home cage   (no incr in lac)  just exposed to home cage but no tone.

examine LAC in basolat amygdala

all groups  have  above average label uptake in the FC  group = fear  conditioned group...

LAC + ZIF in basolater amygdala  ...

note:  not  getting shocked during tone playing...

idea is that  CS  (condit  stim)  reactivates some  synapses that  go from shock to  freezing...

y axis = freezing

as we  weaken  freezing response by extinction  (by letting time pass)

then we also  weaken the correl btwn freezing and LAC + ZIF

how do old memories stay indep of HC  (eg in  HM patient)

can do that  in mice also  eg  anagnostara in 1999 in J neurosci...

Matt Wilson...   mouse runs maze  and  then later  (when sleeping) get replay of HC activity...CA1  activation during consolidation...

****

now, fear condition   ON doxycycline...

put them in home cage  for 2 weeks...

expt result with mice:  do GET overlap of labelling in cells in CA1... high degree of overlap...

so... do the same neurons active during learning become reactivated during recall  YES!

does the strength of memory depend on the strength of circuit reactivation  YES

is there memory relevant off-line activity  YES...

next Q:  are there cell activities that are active during memory???

how do learning and memory work at the  synap level?

LTP story...

increase insertion of new  AMPA receptors...   result from many labs..

LT memories require new protein synthesis ..

idea:  need something new from the nucleus  to stabilize a 1 hour memory and convert it to a multiday/week memory...

he labels entire dendritic arbor   how many spines have  +  receptor cluster...

spines are either thin orf stubby or mushroom shape

looking in CA1

looking at CluR1  after fear conditioning...

fear condit.  no effect in thin or stubby spines

but in mushrroom spines  do  see  signif diff in  new receptor uptake...

context exposure...  just put mouse in cage where he was shocked  but with no shock... or tone

fear conditioning produces a synaptic TAG  (juliet fry and richard morris showed that result)

glutamate receptor is a key cargo that is delivered to the tagged synapses...

takes > 2 hours  for those spines to pick up GluR.

does learning produce circuit specific sturctural changes

LT memory must cause  struc changes...    (eg that one see with enriched enviros (a la Marion Diamond)  etc)

does fear conditioning produce a change in spine numbers?

just do morphology count!

spine numbers  DECREASE with Fear conditioning specifically in the activated neurons!!!  (big surprise)

huge drop!!!!  there IS circuit specificity to this loss!!

mushroom spine decrease is specific to the FC group;

gluR  is  a way to encode info  (BUT, so is  taking AWAY  gluR  cuz perhaps it strengthens the remainder)

if adding new gluReceptors...

can altering  activity in specific neural responses  manip behavior...

DREADD  is a compound that they administer...

(if u stim  halle berry neurons then will the mouse THINK halle berry)

DREADD = designer recep exclu activated by a designer drug...

alexander et al neuron 2009...

CNO  increase neural activity in the 20 hz band...

artificial manip of representations

put into halle berry box...

animals that got  CNO  and got fear conditioning in the original cage

his claim;  CNO firing neurons get incorp  into box B pattern...

but note  CNO  really induces  almost sz like  state!

he claims  internal activity is incorp into new memory

one pattern driven by CNO

and did not freeze in box A...

they need both to  get incorporation...

all the time in your head little patterns are going...

we are taking  one pattern (box A pattern) and forcing it to be ON
by simult giving  CNO;

conclusions...

dispersed neural activity can be incorp into a memory trace...

so, answer to v last question is  ... sort of: really want to do a CR2 expt... channelrhodospsin 2 mouse...

we use CHEF  (hybrid of CR1 and CR2)

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now on to difft brain region...

look at  retrosplenial  cortex  RSC which is connected  to the MTL circuit

MTL = medial temp lobe

RSC  = retrospl cortex...

subiculum is an output tract of  HC

******
y axis = freezing....

light in RSC DOES induce freezing  (abt half of what we saw in fear conditioning but this is wihout  shock
just with the cage)

and it is blocked by doxy infusion during conditioning...

but is freezing  due to activ of neurons...

tagging based context discrimination

it really DOES depend on pattern of cells activated during context conditioning...
(and is not due to freezing assoc neurons)

converted  last question from  maybe to probably...
(to answer the Q.. can altering activity in spec neural ensembles alter encoding?
can we create an artif repres ... answer got promoted by this result from sort of/ maybe to  probably

(look at  tonagawa  work... sparse activation...)

this is all work done at  Scripps Res Instit.

(with genetics work we are not getting all the fos neurons nor all the neurons that are firing  (in amyg) (in answer to Q..

Tom Q:  what does the HC  circuit do?
his explanation...  cue repres  starts say in visual cortex and goes up thru the hierarchy and eventually makes it to RSC
and then around the HC loop...  eventually pattern collapses  when recognized..
(see my explanation below for what he means by "collapses"  (ie gets recognized and pattern crispifies).

tonagawa's freezing is 20%  and his freezing is 20%  (in response to Q abt temporal encoding)
he believes in a rate code for this... (tempor coding was not needed in his research, as it is eg in birdsong work)

at end of his talk I ask him to explain his answer to Tom  abt HC fxn..

here's what he means by collapse  = RECOGNITION

eg  take a really really badly pixilated, noisy representaiton of a CAT... cannot recognize it...
as you remove the noise, all of a sudden.. boom... it collapses:  you recognize the cat.

I ask him abt  attractor states vs  neural ensembles  vs rate coding etc.
he is agonist... does not know

I say... is HC  preserving  binding  during encoding...  yes... he agrees with that..

He has strong feelings against BAM like projects:
1) politically connected people get massive grants  (shud just get  innovation grant)
2) sets up the public for disappoitnment:  we spent 3 Billion: where's the result. now we're disappointed.