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Chapter 7: Synapses

Synapses are the connections between other cells and their compartments. When a compartment reaches threshold, it sends signals to all other compartments which it is connected to.
KeywordValueDescription
SYNAPSE
N/A
Indicates the start of a synapse definition section
TYPE
name(string)
The name which this synapse will be referred to in this simulation
SEED
value(integer)
The random number generator will be seeded with the value specified. This number must be less than zero ( SEED < 0)
SFD_LABEL
name(string)
The short term synaptic dynamic (RSE) to be used
SYN_PSG
name(string)
The synaptic waveform (PSG) to be used
LEARN_LABEL
name(string)
The long term synaptic dynamic (Learn) to be used
HEBB_START
value(real)
Time (in seconds) at which Hebbian learning, specified by LEARN_LABEL, will be turned ON for this synapse. By default, Hebbian is ON from start of simulation.
HEBB_END
value(real)
Time (in seconds) at which Hebbian learning, specified by LEARN_LABEL, will be turned OFF for this synapse.
DATA_LABEL
name(string)
Deprecated. The synaptic conductance (Data) to be used
ABSOLUTE_USE
mean(real)
stdev(real)
The initial value of a Synapse's USE value
RSE_INIT
min(real)
max(real)
The initial value of a Synapse's RSE is one (1) by default. This parameter will vary that value between a min and max value. Note that the RSE can only be a value from 0.0 to 1.0. NCS will automatically limit the RSE if it tries to exceed either of those extremes.
PREV_SPIKE_RANGE
min(real)
max(real)
Synapses keep track of the time at which a last spike occurred. When a simulation begins, the time will be zero (0) for all Synapses by default. Using this parameter allows a Synapse to vary that previous time within a range from the min to max time (in seconds).
MAX_CONDUCT
mean(real)
stdev(real)
Used with SYN_REVERSAL in calculating the current value of a PSG waveform
I(t) = MAX_CONDUCT * CurrentPSGValue * (SYN_REVERSAL - Membrane Voltage)
DELAY
minDelay(real)
maxDelay(real)
A created synapse will be given a delay that falls within the range from minDelay to maxDelay. Before a synapse will output a new waveform, it will wait for the DELAY to expire. This value is given in seconds and will be converted using the FSV. If DISTANCE is turned on, this synaptic delay will combine with the traversal delay.
SYN_REVERSAL
mean(real)
stdev(real)
Used with MAX_CONDUCT in calculating the current value of a PSG waveform
I(t) = MAX_CONDUCT * CurrentPSGValue * (SYN_REVERSAL - Membrane Voltage)
END_SYNAPSE
N/A
Indicates the end of a synapse definition section

Example

SYNAPSE
        TYPE                    ExcF2Hebb+-
        SEED                    -999999
        SFD_LABEL               F2
        SYN_PSG                 PSGexcit
        LEARN_LABEL             +-HEBB
        MAX_CONDUCT             0.01
        DELAY                   0.0008          0.0012
        SYN_REVERSAL            0               0
        ABSOLUTE_USE            0.32            0.0
        RSE_INIT                0.5             0.8
        PREV_SPIKE_RANGE        0.1             0.1
END_SYNAPSE

Turning Hebbian learning ON and OFF Example

Following is an example of Hebbian learning turned on from 200 msec to 600 msec. Remember, by default Hebbian learning is on, so first turn it off.
SYNAPSE
	TYPE			ExcitSyn1_Intra_E1
	SFD_LABEL		NO_SFD
	LEARN_LABEL		POS_NEG_HEBB
	# Turn off Hebbian initially
	HEBB_END		0
	# Turn on Hebbian from 200 msec to 600 msec
	HEBB_START		0.2
	HEBB_END		0.6
	SYN_PSG			PSGexcit
	MAX_CONDUCT		0.020		0.0
	DELAY			0.001		0.001
	SYN_REVERSAL		0		0
	ABSOLUTE_USE		0.250		0.0
END_SYNAPSE
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Last updated Friday 11/2/2007