# 8.7 Mathematical modeling of hippocampal spatial memory with place  (Page 4/6)

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## Stdp

To determine how the weights of the synapses change, we use an STDP model [link] . The spikes times of the pre- and post-synaptic cells are compared, and the smaller the time difference, the more the weight is adjusted. See [link] . The percentage of weight change is determined by

$F\left(\Delta t\right)=\left\{\begin{array}{cc}{A}_{+}{e}^{\Delta t/{\tau }_{+}},\hfill & \Delta t<0\hfill \\ -{A}_{-}{e}^{-\Delta t/{\tau }_{-}},\hfill & \Delta t\ge 0,\hfill \end{array}\right)$

where $\Delta t={t}_{pre}-{t}_{post}$ and ${A}_{+}$ and ${A}_{-}$ scale the maximal amount of change allowed when $\Delta t$ is close to 0 [link] . $F\left(\Delta t\right)$ is depicted in [link] .

In our 120-cell model, we set a lower bound for the weights at $0\phantom{\rule{4pt}{0ex}}mV$ and an upper bound at $5\phantom{\rule{4pt}{0ex}}mV$ . The necessity for an upper weight bound is one of the weaknesses of the STDP model, so Andrew Wu, another member of this PFUG, has done work with other plasticity models. See the link "Mathematical Models of Hippocampal Spatial Memory".

The work with the 120-cell model is all computational. Our results show that each lap, the weight of the synapse from Cell 1 to Cell 2 ( ${w}_{12}$ ) increases toward a set weight bound and the weight of the synapse from Cell 2 to Cell 1 ( ${w}_{21}$ ) decreases to 0 as in [link] . We also see that after 4 laps around the path, the place fields start to shift backward. [link] shows that the spike time of Cell 2 decreases each lap, which is indicative of a backward shift of Cell 2's place field. See IAF120cells1stspks.m .

## Model for analysis

We begin by considering only one place cell which receives input from one external source with constant weight ${w}_{inp}$ at a set interspike interval, $I$ , as depicted in [link] . The following equation gives the voltage $v$ in $mV$ of the cell at time $t$ with $n$ total input spikes:

$\tau {v}^{\text{'}}\left(t\right)=\left({v}_{r}-v\left(t\right)\right)+{w}_{inp}\sum _{i=1}^{n}\delta \left(t-{T}_{i}\right)$

where $\tau =20$ $ms$ is the membrane time constant, ${v}_{r}=-70$ $mV$ is the resting potential, $T$ is the set of input spike times, and $\delta \left(t-{T}_{i}\right)$ is the Dirac delta function. This is a simplification of equation [link] .

anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
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
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
how did you get the value of 2000N.What calculations are needed to arrive at it
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