Date post: | 08-Dec-2015 |
Category: |
Documents |
Upload: | atanu-datta |
View: | 218 times |
Download: | 0 times |
A Matter of Time…
Atanu Datta
Memory
TIME
Object
Space
Odor
Touch
Temporal Sequence of events objects or actions
Time and the Hippocampus
• Time cells– Found in Hippocampus with “no specific
topographic organization”– Code for time in delay intervals.– Increase or decrease their firing rate (FR) to code
for passage of time.– Track time even without active locomotion.
Previous Studies
olfactory temporal order task
CA1 hippocampal cell populations code time, by changes in population activity
Rodents
Visual temporal order task
Time cells coded fo ‘what’ items and in ‘which’ ‘sequential’ order.
Primates
AIM
To characterize incremental timing signals in object place associative learning task.
Time
ObjectSpace
Object Place Combination
O1
O2
+
+
P1
P2
•O1P1, O2P2 Early Release•O1P2, O2P1 Late Release
PARADIGM
Data Acquisition • Specific OP combination is learnt
if Pr(Correct Response) > 0.95Behavioral Training
• MRI guided insertion of microelectrodes via chamber and grid system
• Into Primate hippocampus.
Electrophysiology(n=152 recorded)
139/152 were correct trials
Results• Agnostic ITCs: n=61/139 agnostic; 16/61 ITCs
I
Increased FR n=9 Dec
reas
ed F
R n
=7
Release selective ITCs
• n=78/139, differentiated between trial types
• 43/78 were release selective early (O1P1,O2P2) vs late release (O2P1, O1P2) trials.
• n= 21/43 cells were ITCs.• n=10 FR ‘Incremental Rise’ in
firing rate• n= 11 FR ‘Incremental
Decrease’ in firing)g rate• Eg of early release increasing FR
and late release decreasing FR ITC.
OP selective ITCs• n=31/139 codes for one
particular OP combination out of 4.
• n=26/31 OP selective ITCs.• n=10/26 Incrementally
increased FR .• n=16/26 Incrementally
decreased FR.• Eg. of O2P2 selective
Decreasing FR ITC.
Learning Related Neural Signals
Percentage of ITCS recorded when at least one OP combination was learnt .
Number of OP combinations learnt in sessions in which Ag, RS, and OP ITCs were recorded.
Signals related to task performance
• Compared responses of all three categories ITCs of correct trials vs. incorrect trials.
• Zi = Z-µ (Normalization)
σZi- Z score
Z- Raw firing rateµ- Average firing rateσ- Standard DeviationZ score is a population representation of all PSTH of all trial
types.Error trial- Early release of bar in late release trial; Late release of bar in early trial.
Correct trials vs Error Trials
y-=mx+c; m =tan Ө
Release selective ITCs showed significantly greater differences in incremental tuning when comparing correct vs incorrect trials than Ag ITCs and OP ITCs.
Ag. ITC RS ITC
OP ITC
Summary• Studied delay activity of hippocampal ITCs in OP learning
task.• ITCs increased or decre3ased FR with passage of time.• Agnostic, Release Selective and OP selective ITCs were
characterized.• Release and OP selective integrated time and context.• RS and OP selective ITCs fired significantly more for learning
OP combinations than agnostic ITCs.• Thus, RS and OP ITCs are responsible for learning OP
combinations.• All three categories of ITCs showed decreased firing rate in
error trials than in correct trials.• Thus ITCs also code for task performance.
THANK YOU