<s>
In	O
neuroscience	O
and	O
computer	B-General_Concept
science	I-General_Concept
,	O
synaptic	B-Algorithm
weight	I-Algorithm
refers	O
to	O
the	O
strength	O
or	O
amplitude	B-Application
of	O
a	O
connection	O
between	O
two	O
nodes	O
,	O
corresponding	O
in	O
biology	O
to	O
the	O
amount	O
of	O
influence	O
the	O
firing	B-Algorithm
of	O
one	O
neuron	O
has	O
on	O
another	O
.	O
</s>
<s>
The	O
term	O
is	O
typically	O
used	O
in	O
artificial	B-Architecture
and	O
biological	B-General_Concept
neural	I-General_Concept
network	I-General_Concept
research	O
.	O
</s>
<s>
where	O
the	O
rows	O
of	O
the	O
synaptic	O
matrix	O
represent	O
the	O
vector	O
of	O
synaptic	B-Algorithm
weights	I-Algorithm
for	O
the	O
output	O
indexed	O
by	O
.	O
</s>
<s>
Computationally	O
,	O
this	O
means	O
that	O
if	O
a	O
large	O
signal	O
from	O
one	O
of	O
the	O
input	O
neurons	O
results	O
in	O
a	O
large	O
signal	O
from	O
one	O
of	O
the	O
output	O
neurons	O
,	O
then	O
the	O
synaptic	B-Algorithm
weight	I-Algorithm
between	O
those	O
two	O
neurons	O
will	O
increase	O
.	O
</s>
<s>
The	O
rule	O
is	O
unstable	O
,	O
however	O
,	O
and	O
is	O
typically	O
modified	O
using	O
such	O
variations	O
as	O
Oja	B-Algorithm
's	I-Algorithm
rule	I-Algorithm
,	O
radial	B-Algorithm
basis	I-Algorithm
functions	I-Algorithm
or	O
the	O
backpropagation	B-Algorithm
algorithm	O
.	O
</s>
<s>
For	O
biological	B-General_Concept
networks	O
,	O
the	O
effect	O
of	O
synaptic	B-Algorithm
weights	I-Algorithm
is	O
not	O
as	O
simple	O
as	O
for	O
linear	O
neurons	O
or	O
Hebbian	O
learning	O
.	O
</s>
<s>
For	O
the	O
basic	O
pyramidal	O
neuron	O
,	O
the	O
input	O
signal	O
is	O
carried	O
by	O
the	O
axon	B-Algorithm
,	O
which	O
releases	O
neurotransmitter	O
chemicals	O
into	O
the	O
synapse	B-Application
which	O
is	O
picked	O
up	O
by	O
the	O
dendrites	O
of	O
the	O
next	O
neuron	O
,	O
which	O
can	O
then	O
generate	O
an	O
action	B-Algorithm
potential	I-Algorithm
which	O
is	O
analogous	O
to	O
the	O
output	O
signal	O
in	O
the	O
computational	O
case	O
.	O
</s>
<s>
The	O
synaptic	B-Algorithm
weight	I-Algorithm
in	O
this	O
process	O
is	O
determined	O
by	O
several	O
variable	O
factors	O
:	O
</s>
<s>
How	O
well	O
the	O
input	O
signal	O
propagates	O
through	O
the	O
axon	B-Algorithm
(	O
see	O
myelination	O
)	O
,	O
</s>
<s>
The	O
amount	O
of	O
neurotransmitter	O
released	O
into	O
the	O
synapse	B-Application
and	O
the	O
amount	O
that	O
can	O
be	O
absorbed	O
in	O
the	O
following	O
cell	O
(	O
determined	O
by	O
the	O
number	O
of	O
AMPA	O
and	O
NMDA	O
receptors	O
on	O
the	O
cell	O
membrane	O
and	O
the	O
amount	O
of	O
intracellular	O
calcium	O
and	O
other	O
ions	O
)	O
,	O
</s>
<s>
The	O
number	O
of	O
such	O
connections	O
made	O
by	O
the	O
axon	B-Algorithm
to	O
the	O
dendrites	O
,	O
</s>
<s>
The	O
changes	O
in	O
synaptic	B-Algorithm
weight	I-Algorithm
that	O
occur	O
is	O
known	O
as	O
synaptic	O
plasticity	O
,	O
and	O
the	O
process	O
behind	O
long-term	O
changes	O
(	O
long-term	O
potentiation	O
and	O
depression	O
)	O
is	O
still	O
poorly	O
understood	O
.	O
</s>
<s>
Hebb	O
's	O
original	O
learning	O
rule	O
was	O
originally	O
applied	O
to	O
biological	B-General_Concept
systems	O
,	O
but	O
has	O
had	O
to	O
undergo	O
many	O
modifications	O
as	O
a	O
number	O
of	O
theoretical	O
and	O
experimental	O
problems	O
came	O
to	O
light	O
.	O
</s>
