.. currentmodule:: brian

.. index::
   pair: example usage; NeuronGroup
   pair: example usage; run
   pair: example usage; raster_plot
   pair: example usage; Connection
   pair: example usage; SpikeMonitor
   pair: example usage; STDP

.. _example-twister_FriedemannZenke:

Example: FriedemannZenke (twister)
==================================

Friedemann Zenke's winning entry for the 2012 Brian twister.

::

    # ###########################################
    #
    # Inhibitory synaptic plasticity in a recurrent network model 
    # (F. Zenke, 2011)
    #
    # Adapted from: 
    # Vogels, T. P., H. Sprekeler, F. Zenke, C. Clopath, and W. Gerstner. 
    # 'Inhibitory Plasticity Balances Excitation and Inhibition in Sensory
    # Pathways and Memory Networks.' Science (November 10, 2011). 
    #
    # ###########################################
    
    from brian import *
    
    # ###########################################
    # Defining network model parameters
    # ###########################################
    
    NE = 8000          # Number of excitatory cells
    NI = NE/4          # Number of inhibitory cells 
    
    w = 1.*nS           # Basic weight unit
    tau_ampa = 5.0*ms   # Glutamatergic synaptic time constant
    tau_gaba = 10.0*ms  # GABAergic synaptic time constant
    epsilon = 0.02      # Sparseness of synaptic connections
    
    eta = 1e-2          # Learning rate
    tau_stdp = 20*ms    # STDP time constant
    
    simtime = 10*second # Simulation time
    
    # ###########################################
    # Neuron model
    # ###########################################
    
    gl = 10.0*nsiemens   # Leak conductance
    el = -60*mV          # Resting potential
    er = -80*mV          # Inhibitory reversal potential
    vt = -50.*mV         # Spiking threshold
    memc = 200.0*pfarad  # Membrane capacitance
    bgcurrent = 200*pA   # External current
    
    eqs_neurons='''
    dv/dt=(-gl*(v-el)-(g_ampa*w*v+g_gaba*(v-er)*w)+bgcurrent)/memc : volt
    dg_ampa/dt = -g_ampa/tau_ampa : 1
    dg_gaba/dt = -g_gaba/tau_gaba : 1
    '''
    
    # ###########################################
    # Initialize neuron group
    # ###########################################
    
    neurons=NeuronGroup(NE+NI,model=eqs_neurons,threshold=vt,reset=el,refractory=5*ms)
    Pe=neurons.subgroup(NE)
    Pi=neurons.subgroup(NI)
    
    # ###########################################
    # Connecting the network 
    # ###########################################
    
    con_e = Connection(Pe,neurons,'g_ampa',weight=0.3,sparseness=epsilon)
    con_ie = Connection(Pi,Pe,'g_gaba',weight=1e-10,sparseness=epsilon)
    con_ii = Connection(Pi,Pi,'g_gaba',weight=3,sparseness=epsilon)
    
    # ###########################################
    # Setting up monitors
    # ###########################################
    
    sm = SpikeMonitor(Pe)
    
    # ###########################################
    # Run without plasticity
    # ###########################################
    
    run(1*second)
    
    # ###########################################
    # Inhibitory Plasticity
    # ###########################################
    
    alpha = 3*Hz*tau_stdp*2  # Target rate parameter
    gmax = 100               # Maximum inhibitory weight
    
    eqs_stdp_inhib = '''
    dA_pre/dt=-A_pre/tau_stdp : 1
    dA_post/dt=-A_post/tau_stdp : 1
    '''
    
    stdp_ie = STDP(con_ie, eqs=eqs_stdp_inhib, pre='A_pre+=1.; w+=(A_post-alpha)*eta;',
            post='A_post+=1.; w+=A_pre*eta;', wmax=gmax)
    
    # ###########################################
    # Run with plasticity
    # ###########################################
    
    run(simtime-1*second,report='text')
    
    # ###########################################
    # Make plots
    # ###########################################
    
    subplot(211)
    raster_plot(sm,ms=1.)
    title("Before")
    xlabel("")
    xlim(0.8*1e3,1*1e3)
    subplot(212)
    raster_plot(sm,ms=1.)
    title("After")
    xlim((simtime-0.2*second)*1e3,simtime*1e3)
    show()