neuron_model_izh_impl.h File Reference

Izhekevich neuron type. More...

#include "neuron_model.h"

Go to the source code of this file.

Data Structures
struct	neuron_params_t
	definition of neuron parameters More...
struct	neuron_t
	definition for LIF neuron state More...

Functions
static void	neuron_model_initialise (neuron_t *state, neuron_params_t *params, uint32_t n_steps_per_timestep)
static void	neuron_model_save_state (neuron_t *state, neuron_params_t *params)
static void	rk2_kernel_midpoint (REAL h, neuron_t *neuron, REAL input_this_timestep)
	Midpoint is best balance between speed and accuracy so far.
static state_t	neuron_model_state_update (uint16_t num_excitatory_inputs, const input_t *exc_input, uint16_t num_inhibitory_inputs, const input_t *inh_input, input_t external_bias, REAL current_offset, neuron_t *restrict neuron)
	primary function called in timer loop after synaptic updates
static void	neuron_model_has_spiked (neuron_t *restrict neuron)
	Indicates that the neuron has spiked.
static state_t	neuron_model_get_membrane_voltage (const neuron_t *neuron)
	get the neuron membrane voltage for a given neuron parameter set
static void	neuron_model_print_state_variables (const neuron_t *neuron)
static void	neuron_model_print_parameters (const neuron_t *neuron)

Variables
static const REAL	SIMPLE_TQ_OFFSET = REAL_CONST(1.85)
	For linear membrane voltages, 1.5 is the correct value. However with actual membrane voltage behaviour and tested over an wide range of use cases 1.85 gives slightly better spike timings.
static const REAL	MAGIC_MULTIPLIER = REAL_CONST(0.040008544921875)
	The original model uses 0.04, but this (1 ULP larger?) gives better numeric stability.

Detailed Description

Izhekevich neuron type.

Definition in file neuron_model_izh_impl.h.

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Data Structure Documentation

neuron_params_t

struct neuron_params_t

definition of neuron parameters

The state parameters of an Izhekevich model neuron.

definition for LIF neuron parameters

Definition at line 47 of file neuron_impl_stoc_exp.h.

Data Fields
UREAL	tau_ms	The tau value of the neuron.
UREAL	time_step	The timestep of the neuron being used. The time step in milliseconds. current timestep in ms
REAL	bias	The bias value.
uint32_t	refract_init	The initial refractory timer.
mars_kiss64_seed_t	random_seed	Random seed to use.
REAL	v_init	The initial membrane voltage.
REAL	v_reset	The reset membrane voltage after a spike.
UREAL	tau	The tau value of the neuron, multiplied by 2^v to get probability.
UREAL	tau_refract	The refractory period of the neuron in milliseconds. The refractory period of the neuron, in ms.
REAL	alpha	The alpha value of the neuron prob = (2^(-2^(alpha x voltage)))
REAL	V_init	membrane voltage [mV]
REAL	c_m	membrane capacitance [nF]
REAL	tau_m	membrane decay time constant
REAL	I_offset	offset current [nA]
REAL	V_reset	post-spike reset membrane voltage [mV]
REAL	T_refract_ms	refractory time of neuron [ms]
int32_t	refract_timer_init	initial refractory timer value (saved)
REAL	time_step	The time step in milliseconds. current timestep in ms
REAL	A
REAL	B
REAL	C
REAL	D
REAL	V
REAL	U
REAL	next_h	next value of this_h (saved)
REAL	V_rest	membrane resting voltage [mV]

neuron_t

struct neuron_t

definition for LIF neuron state

The state variables of an Izhekevich model neuron.

Definition at line 53 of file neuron_model_if_trunc.h.

Data Fields
REAL	V_membrane	membrane voltage [mV]
REAL	R_membrane	membrane resistance [MOhm]
REAL	I_offset	offset current [nA]
int32_t	refract_timer	countdown to end of next refractory period [timesteps]
REAL	V_reset	post-spike reset membrane voltage [mV]
int32_t	T_refract	refractory time of neuron [timesteps]
REAL	A
REAL	B
REAL	C
REAL	D
REAL	V
REAL	U
REAL	this_h	current timestep
REAL	reset_h	timestep to reset to when not just spiked
REAL	V_rest	membrane resting voltage [mV]
REAL	exp_TC	'fixed' computation parameter - time constant multiplier for closed-form solution exp(-(machine time step in ms)/(R * C)) [.]

Function Documentation

neuron_model_initialise()

static void neuron_model_initialise ( neuron_t *  state, neuron_params_t *  params, uint32_t  n_steps_per_timestep  )

inlinestatic

Definition at line 68 of file neuron_model_izh_impl.h.

neuron_model_save_state()

static void neuron_model_save_state ( neuron_t *  state, neuron_params_t *  params  )

inlinestatic

Definition at line 81 of file neuron_model_izh_impl.h.

rk2_kernel_midpoint()

static void rk2_kernel_midpoint ( REAL  h, neuron_t *  neuron, REAL  input_this_timestep  )

inlinestatic

Midpoint is best balance between speed and accuracy so far.

From ODE solver comparison work, paper shows that Trapezoid version gives better accuracy at small speed cost

Parameters

[in]	h	threshold
[in,out]	neuron	The model being updated
[in]	input_this_timestep	the input

Definition at line 129 of file neuron_model_izh_impl.h.

neuron_model_state_update()

static state_t neuron_model_state_update ( uint16_t  num_excitatory_inputs, const input_t *  exc_input, uint16_t  num_inhibitory_inputs, const input_t *  inh_input, input_t  external_bias, REAL  current_offset, neuron_t *restrict  neuron  )

inlinestatic

primary function called in timer loop after synaptic updates

Parameters

[in]	num_excitatory_inputs	Number of excitatory receptor types.
[in]	exc_input	Pointer to array of inputs per receptor type received this timer tick that produce a positive reaction within the neuron in terms of stimulation.
[in]	num_inhibitory_inputs	Number of inhibitory receptor types.
[in]	inh_input	Pointer to array of inputs per receptor type received this timer tick that produce a negative reaction within the neuron in terms of stimulation.
[in]	external_bias	This is the intrinsic plasticity which could be used for ac, noisy input etc etc. (general purpose input)
[in,out]	neuron	the pointer to a neuron parameter struct which contains all the parameters for a specific neuron

Returns

the value to be compared with a threshold value to determine if the neuron has spiked

Definition at line 166 of file neuron_model_izh_impl.h.

neuron_model_has_spiked()

static void neuron_model_has_spiked ( neuron_t *restrict  neuron )

inlinestatic

Indicates that the neuron has spiked.

Parameters

[in,out]

neuron

pointer to a neuron parameter struct which contains all the parameters for a specific neuron

Definition at line 193 of file neuron_model_izh_impl.h.

neuron_model_get_membrane_voltage()

static state_t neuron_model_get_membrane_voltage ( const neuron_t *  neuron )

inlinestatic

get the neuron membrane voltage for a given neuron parameter set

Parameters

[in]

neuron

a pointer to a neuron parameter struct which contains all the parameters for a specific neuron

Returns

the membrane voltage for a given neuron with the neuron parameters specified in neuron

Definition at line 209 of file neuron_model_izh_impl.h.

neuron_model_print_state_variables()

static void neuron_model_print_state_variables ( const neuron_t *  neuron )

inlinestatic

Definition at line 213 of file neuron_model_izh_impl.h.

neuron_model_print_parameters()

static void neuron_model_print_parameters ( const neuron_t *  neuron )

inlinestatic

Definition at line 219 of file neuron_model_izh_impl.h.

Variable Documentation

SIMPLE_TQ_OFFSET

const REAL SIMPLE_TQ_OFFSET = REAL_CONST(1.85)

static

For linear membrane voltages, 1.5 is the correct value. However with actual membrane voltage behaviour and tested over an wide range of use cases 1.85 gives slightly better spike timings.

Definition at line 91 of file neuron_model_izh_impl.h.

MAGIC_MULTIPLIER

const REAL MAGIC_MULTIPLIER = REAL_CONST(0.040008544921875)

static

The original model uses 0.04, but this (1 ULP larger?) gives better numeric stability.

Thanks to Mantas Mikaitis for this!

Definition at line 119 of file neuron_model_izh_impl.h.