Object Type:	ddsyn

Description:	modified synchan with table front end to transform voltage
		to activation, for dendro-dendritic synapses.  Calculates
		channel current therefore needs membrane state.

Author:		U. S. Bhalla, Caltech (5/91)

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ELEMENT PARAMETERS

DataStructure:	dd_syn_type  [in src/olf/olf_struct.h]

Size:		164 bytes

Fields:		Gk		channel conductance
		Ik		channel current
		Ek		channel reversal potential
		gmax		maximum conductance
                tau1		open time constant of channel activation
		tau2		close time constant of channel activation
                transf		table for transform from Vm to activation;
				usual interpolation element with the normal
				set of fields; set up using TABCREATE, filled
				by indexing as usual, and interpolated using
				TABFILL
		activation	channel activation; set either by a table
				lookup of the transform of the incoming
				VOLTAGE message or by synaptic input
		transf_alloced	flag for allocation of transform
		X		state variable for time response
		Y		state variable for time response

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SIMULATION PARAMETERS

Function:	DDSyn  [in src/olf/dd_syn.c]

Classes:	segment, channel

Actions:	INIT
		PROCESS
		RESET
		CHECK
		SET
		DUMP
		SAVE2
		RESTORE2
		TABCREATE
		TABFILL

Messages:	VOLTAGE voltage			[tells channel what membrane
						potential is]

                ACTIVATION activation		[sends activation directly to
						channel; sums linearly with
						other ACTIVATION input and
						transformed V_PRESYN input]

                V_PRESYN presynaptic-voltage	[sends presynaptic voltage to
						transform table; sums linearly
						at output of table, so
						multiple V_PRESYN inputs are
						first transformed, then their
						activations are summed]

                RAND_ACTIVATION			[rather than sending direct
		  probability  amplitude	activation signal, specifies
						probability (from 0 to 1) that
						activation of size amplitude
						will occur at synapse (useful
						for sending random synaptic
						input to synapse)]

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Notes:		Dendrodendritic synapse with tabulated transform
		from presyn potential to postsyn activation.
		The table for the transform is created using tabcreate
		and is shared with all copies of the element

		The ddsyn element is the equivalent of a synchan element
		with a tabulated transform from input voltage to channel
		activation. This serves as a way of representing
		dendro-dendritic synapses.  The usual fields and messages for
		the synchan element remain available. The table entries are
		filled in the usual ways from the script interface, and can be
		shared between ddsyn elements.

Example:	Here we create a ddsyn channel to act as the synaptic input
		for granule cells in an olfactory bulb model.

		    // for dd, ax, and centrif inputs
		    create      ddsyn   glu_gran_usb
		    call glu_gran_usb TABCREATE 10 -0.070   0.05
		    setfield  glu_gran_usb \
			Ek          {EGlu} \
			tau1        4.0e-3 \   // sec
			tau2        6.0e-3 \   // sec
			gmax        {GGlu} \   // Siemens
		    // Setting up the table for transforming
		    // from presyn Vm to activation
			transf->table[0] 0 \
			transf->table[1] 0.05 \
			transf->table[2] 0.1 \
			transf->table[3] 0.2 \
			transf->table[4] 0.5 \
			transf->table[5] 0.7 \
			transf->table[6] 0.8 \
			transf->table[7] 0.9 \
			transf->table[8] 0.95 \
			transf->table[9] 0.98 \
			transf->table[10] 1
		    call glu_gran_usb TABFILL 1000 0
				
See also:  Scripts/examples/ddsyn

