stdp_nn_symm_synapse.h

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/*
 *  stdp_nn_symm_synapse.h
 *
 *  This file is part of NEST.
 *
 *  Copyright (C) 2004 The NEST Initiative
 *
 *  NEST is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  NEST is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with NEST.  If not, see <http://www.gnu.org/licenses/>.
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 */
 
#ifndef STDP_NN_SYMM_SYNAPSE_H
#define STDP_NN_SYMM_SYNAPSE_H
 
// C++ includes:
#include <cmath>
 
// Includes from nestkernel:
#include "common_synapse_properties.h"
#include "connection.h"
#include "connector_model.h"
#include "event.h"
 
 
namespace nest
{
 
/* BeginUserDocs: synapse, stdp
 
Short description
+++++++++++++++++
 
Synapse type for spike-timing dependent plasticity with symmetric nearest-neighbour spike pairing scheme
 
Description
+++++++++++
 
``stdp_nn_symm_synapse`` is a connector to create synapses with spike time
dependent plasticity with the symmetric nearest-neighbour spike pairing
scheme :footcite:p:`Morrison2007c`.
 
When a presynaptic spike occurs, it is taken into account in the depression
part of the STDP weight change rule with the nearest preceding postsynaptic
one, and when a postsynaptic spike occurs, it is accounted in the
facilitation rule with the nearest preceding presynaptic one (instead of
pairing with all spikes, like in ``stdp_synapse``). For a clear illustration of
this scheme see fig. 7A in :footcite:p:`Morrison2008`.
 
The pairs exactly coinciding (so that ``presynaptic_spike == postsynaptic_spike
+ dendritic_delay``), leading to zero ``delta_t``, are discarded. In this case the
concerned pre/postsynaptic spike is paired with the second latest preceding
post/presynaptic one (for example, ``pre=={10 ms; 20 ms}`` and ``post=={20 ms}`` will
result in a potentiation pair 20-to-10).
 
The implementation involves two additional variables - presynaptic and
postsynaptic traces :footcite:p:`Morrison2008`. The presynaptic trace decays exponentially over
time with the time constant ``tau_plus`` and increases to 1 on a pre-spike
occurrence. The postsynaptic trace (implemented on the postsynaptic neuron
side) decays with the time constant ``tau_minus`` and increases to 1 on a
post-spike occurrence.
 
.. warning::
 
   This synaptic plasticity rule does not take
   :ref:`precise spike timing <sim_precise_spike_times>` into
   account. When calculating the weight update, the precise spike time part
   of the timestamp is ignored.
 
Parameters
++++++++++
 
========= =======  ======================================================
 tau_plus  ms      Time constant of STDP window, potentiation
                   (tau_minus defined in postsynaptic neuron)
 lambda    real    Step size
 alpha     real    Asymmetry parameter (scales depressing increments as
                   alpha*lambda)
 mu_plus   real    Weight dependence exponent, potentiation
 mu_minus  real    Weight dependence exponent, depression
 Wmax      real    Maximum allowed weight
========= =======  ======================================================
 
Transmits
+++++++++
 
SpikeEvent
 
References
++++++++++
 
.. footbibliography::
 
See also
++++++++
 
stdp_synapse
 
Examples using this model
+++++++++++++++++++++++++
 
.. listexamples:: stdp_nn_symm_synapse
 
EndUserDocs */
 
// connections are templates of target identifier type (used for pointer /
// target index addressing) derived from generic connection template
 
void register_stdp_nn_symm_synapse( const std::string& name );
 
template < typename targetidentifierT >
class stdp_nn_symm_synapse : public Connection< targetidentifierT >
{
 
public:
  typedef CommonSynapseProperties CommonPropertiesType;
  typedef Connection< targetidentifierT > ConnectionBase;
 
  static constexpr ConnectionModelProperties properties = ConnectionModelProperties::HAS_DELAY
    | ConnectionModelProperties::IS_PRIMARY | ConnectionModelProperties::SUPPORTS_HPC
    | ConnectionModelProperties::SUPPORTS_LBL;
 
  stdp_nn_symm_synapse();
 
 
  stdp_nn_symm_synapse( const stdp_nn_symm_synapse& ) = default;
  stdp_nn_symm_synapse& operator=( const stdp_nn_symm_synapse& ) = default;
 
  // Explicitly declare all methods inherited from the dependent base
  // ConnectionBase. This avoids explicit name prefixes in all places these
  // functions are used. Since ConnectionBase depends on the template parameter,
  // they are not automatically found in the base class.
  using ConnectionBase::get_delay;
  using ConnectionBase::get_delay_steps;
  using ConnectionBase::get_rport;
  using ConnectionBase::get_target;
 
  void get_status( Dictionary& d ) const;
 
  void set_status( const Dictionary& d, ConnectorModel& cm );
 
  bool send( Event& e, size_t t, const CommonSynapseProperties& cp );
 
 
  class ConnTestDummyNode : public ConnTestDummyNodeBase
  {
  public:
    // Ensure proper overriding of overloaded virtual functions.
    // Return values from functions are ignored.
    using ConnTestDummyNodeBase::handles_test_event;
    size_t
    handles_test_event( SpikeEvent&, size_t ) override
    {
      return invalid_port;
    }
  };
 
  void
  check_connection( Node& s, Node& t, size_t receptor_type, const CommonPropertiesType& )
  {
    ConnTestDummyNode dummy_target;
 
    ConnectionBase::check_connection_( dummy_target, s, t, receptor_type );
 
    t.register_stdp_connection( t_lastspike_ - get_delay(), get_delay() );
  }
 
  void
  set_weight( double w )
  {
    weight_ = w;
  }
 
private:
  double
  facilitate_( double w, double kplus )
  {
    double norm_w = ( w / Wmax_ ) + ( lambda_ * std::pow( 1.0 - ( w / Wmax_ ), mu_plus_ ) * kplus );
    return norm_w < 1.0 ? norm_w * Wmax_ : Wmax_;
  }
 
  double
  depress_( double w, double kminus )
  {
    double norm_w = ( w / Wmax_ ) - ( alpha_ * lambda_ * std::pow( w / Wmax_, mu_minus_ ) * kminus );
    return norm_w > 0.0 ? norm_w * Wmax_ : 0.0;
  }
 
  // data members of each connection
  double weight_;
  double tau_plus_;
  double lambda_;
  double alpha_;
  double mu_plus_;
  double mu_minus_;
  double Wmax_;
 
  double t_lastspike_;
};
 
template < typename targetidentifierT >
constexpr ConnectionModelProperties stdp_nn_symm_synapse< targetidentifierT >::properties;
 
template < typename targetidentifierT >
inline bool
stdp_nn_symm_synapse< targetidentifierT >::send( Event& e, size_t t, const CommonSynapseProperties& )
{
  // synapse STDP depressing/facilitation dynamics
  double t_spike = e.get_stamp().get_ms();
 
  // use accessor functions (inherited from Connection< >) to obtain delay and
  // target
  Node* target = get_target( t );
  double dendritic_delay = get_delay();
 
  // get spike history in relevant range (t1, t2] from postsynaptic neuron
  std::deque< histentry >::iterator start;
  std::deque< histentry >::iterator finish;
 
  // For a new synapse, t_lastspike_ contains the point in time of the last
  // spike. So we initially read the
  // history(t_last_spike - dendritic_delay, ..., T_spike-dendritic_delay]
  // which increases the access counter for these entries.
  // At registration, all entries' access counters of
  // history[0, ..., t_last_spike - dendritic_delay] have been
  // incremented by ArchivingNode::register_stdp_connection(). See bug #218 for
  // details.
  target->get_history( t_lastspike_ - dendritic_delay, t_spike - dendritic_delay, &start, &finish );
  // facilitation due to postsynaptic spikes since the last pre-synaptic spike
  double minus_dt;
  while ( start != finish )
  {
    minus_dt = t_lastspike_ - ( start->t_ + dendritic_delay );
    ++start;
 
    // get_history() should make sure that
    // start->t_ > t_lastspike_ - dendritic_delay, i.e. minus_dt < 0
    assert( minus_dt < -1.0 * kernel().connection_manager.get_stdp_eps() );
 
    weight_ = facilitate_( weight_, std::exp( minus_dt / tau_plus_ ) );
  }
 
  // depression due to the new pre-synaptic spike
  double nearest_neighbor_Kminus;
  double value_to_throw_away;  // discard Kminus and Kminus_triplet here
  target->get_K_values( t_spike - dendritic_delay, value_to_throw_away, nearest_neighbor_Kminus, value_to_throw_away );
  weight_ = depress_( weight_, nearest_neighbor_Kminus );
 
  e.set_receiver( *target );
  e.set_weight( weight_ );
  // use accessor functions (inherited from Connection< >) to obtain delay in
  // steps and rport
  e.set_delay_steps( get_delay_steps() );
  e.set_rport( get_rport() );
  e();
 
  t_lastspike_ = t_spike;
 
  return true;
}
 
 
template < typename targetidentifierT >
stdp_nn_symm_synapse< targetidentifierT >::stdp_nn_symm_synapse()
  : ConnectionBase()
  , weight_( 1.0 )
  , tau_plus_( 20.0 )
  , lambda_( 0.01 )
  , alpha_( 1.0 )
  , mu_plus_( 1.0 )
  , mu_minus_( 1.0 )
  , Wmax_( 100.0 )
  , t_lastspike_( 0.0 )
{
}
 
template < typename targetidentifierT >
void
stdp_nn_symm_synapse< targetidentifierT >::get_status( Dictionary& d ) const
{
  ConnectionBase::get_status( d );
  d[ names::weight ] = weight_;
  d[ names::tau_plus ] = tau_plus_;
  d[ names::lambda ] = lambda_;
  d[ names::alpha ] = alpha_;
  d[ names::mu_plus ] = mu_plus_;
  d[ names::mu_minus ] = mu_minus_;
  d[ names::Wmax ] = Wmax_;
  d[ names::size_of ] = static_cast< long >( sizeof( *this ) );
}
 
template < typename targetidentifierT >
void
stdp_nn_symm_synapse< targetidentifierT >::set_status( const Dictionary& d, ConnectorModel& cm )
{
  ConnectionBase::set_status( d, cm );
  d.update_value( names::weight, weight_ );
  d.update_value( names::tau_plus, tau_plus_ );
  d.update_value( names::lambda, lambda_ );
  d.update_value( names::alpha, alpha_ );
  d.update_value( names::mu_plus, mu_plus_ );
  d.update_value( names::mu_minus, mu_minus_ );
  d.update_value( names::Wmax, Wmax_ );
 
  // check if weight_ and Wmax_ have the same sign
  if ( std::signbit( weight_ ) != std::signbit( Wmax_ ) )
  {
    throw BadProperty( "Weight and Wmax must have same sign." );
  }
}
 
}  // of namespace nest
 
#endif  // of #ifndef STDP_NN_SYMM_SYNAPSE_H