# 8.6 Mathematical models of hippocampal spatial memory  (Page 11/13)

 Page 11 / 13

We also analyze multiplicative STDP as an improved variation of STDP. We display the forward and backward synaptic weights as a function of lap in [link] .

We observe an asymptotic trend of the weight changes in this regime as opposed to the stepwise form of weight changes in regular, additive STDP. We also depict the place field backward shift in [link] .

When using multiplicative STDP, we see a faster backward shift in earlier laps due to the faster initial increase in synaptic weight. This shift also slows down significantly in later laps due to the slowed increase in weights, leading to final place field stabilization. This trend appears to agree with the nature of the backward shift in experimental results [link] . While this is a slightly improved fit to experimental data as opposed to STDP, the weight bounds are directly incorporated into the weight modification equations, making it a better approximation of results than an explanation of the mechanisms behind synaptic plasticity.

Having explained the advantages and disadvantages of STDP, we now look at CaDP and compare its simulation results with STDP. First, we will depict the changes in calcium concentrations in different synapses to better illustrate the mechanisms behind CaDP.

The plot above shows calcium changes in the forward connection from cell 1 to cell 2 and the two counterclockwise connections associated with cell 1. We observe that the clockwise synapse reaches a calcium level above the LTP threshold due to effective pre-post firing. We also notice that presynaptic firing without postsynaptic response results in LTD calcium levels. Also notice that the initial increase in calcium concentration from baseline levels results from the peak in the $f$ function as a result from presynaptic spiking, and the subsequent increases of calcium into the LTP region are a result from postsynaptic feedback from the back-propagating action potential. Furthermore, persistent postsynaptic cell firing following presynaptic stimulus causes a sustained LTP calcium concentration and allows for increased potentiation of synaptic weights.

The changes in calcium levels yield the following weight changes and backward shift over the simulation as depicted below in [link] .

These plots show that CaDP is able to reproduce the same weight changes and backward shift found in STDP. However, there are a couple of slight differences. The weight changes in STDP result only following the occurence of a postsynaptic spike. However, in CaDP, weights are constantly being changed as a function of calcium levels. Furthermore, we note that the depression of the backward connections occurs in an almost entirely different manner than in STDP: in STDP, LTD was an inherent part of the learning rule whenever a postsynaptic spike preceded a presynaptic spike. In CaDP, LTD results from the absence of or extended time between the postsynaptic spike following presynaptic stimulation. As such, the second LTD window is an essential consequence of the CaDP model in the depression of synaptic weights.

What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
how did you get the value of 2000N.What calculations are needed to arrive at it
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