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name brian2-simulation description Use this Skill to simulate spiking neural networks with Brian2: LIF/AdEx neurons, STDP, recurrent networks, raster plots, and mean-field analysis.
tags ["neuroscience","computational-neuroscience","brian2","spiking-networks","neural-simulation"] version 1.0.0 authors [{"name":"Rosetta Skills Contributors","github":"@xjtulyc"}] license MIT platforms ["claude-code","codex","gemini-cli","cursor"] dependencies {"python":["brian2>=2.5","numpy>=1.24","matplotlib>=3.7","scipy>=1.11","pandas>=2.0"]} last_updated 2026-03-17 status stable
Brian2 Spiking Neural Network Simulation
One-line summary : Simulate biologically plausible spiking neural networks with Brian2: LIF, AdEx, Hodgkin-Huxley neurons, STDP plasticity, and recurrent network dynamics.
When to Use This Skill
When simulating integrate-and-fire or conductance-based neuron models
When studying spike-timing-dependent plasticity (STDP)
When implementing recurrent excitatory-inhibitory networks
When generating raster plots and firing rate analyses
When fitting mean-field equations to network simulations
When comparing neural coding hypotheses (rate vs. temporal)
Trigger keywords : Brian2, spiking neural network, integrate-and-fire, LIF, AdEx, Hodgkin-Huxley, STDP, synaptic plasticity, raster plot, neural simulation
Background & Key Concepts
Leaky Integrate-and-Fire (LIF) Model
$$
\tau_m \frac{dV}{dt} = -(V - V_\text{rest}) + R \cdot I(t)
$$
When $V \geq V_\text{thresh}$: fire a spike, reset $V = V_\text{reset}$.
Parameters: $\tau_m$ = membrane time constant, $R$ = membrane resistance, $V_\text{rest}$ = resting potential.
Adaptive Exponential (AdEx) Model
Adds spike-triggered adaptation:
$$
C \frac{dV}{dt} = -g_L(V - E_L) + g_L \Delta_T e^{(V-V_T)/\Delta_T} - w + I
$$
$$
\tau_w \frac{dw}{dt} = a(V - E_L) - w
$$
Spike-Timing-Dependent Plasticity (STDP)
Synaptic weight changes based on spike timing:
$$
\Delta w = \begin{cases} A_+ e^{-|\Delta t|/\tau_+} & \text{if } t_\text{post} > t_\text{pre} \ -A_- e^{-|\Delta t|/\tau_-} & \text{if } t_\text{post} < t_\text{pre} \end{cases}
$$
Environment Setup
Install Dependencies
pip install brian2>=2.5 numpy>=1.24 matplotlib>=3.7 scipy>=1.11 pandas>=2.0
Verify Installation
import brian2 as b2
print (f"Brian2 version: {b2.__version__} " )
b2.start_scope()
G = b2.NeuronGroup(10 , "dv/dt = -v/(10*ms) : 1" , threshold="v>0.9" , reset="v=0" )
print ("Brian2 functional" )
Core Workflow
Step 1: Single Neuron Models import brian2 as b2
import numpy as np
import matplotlib.pyplot as plt
b2.start_scope()
tau = 10 * b2.ms
Vr = -65 * b2.mV
Vt = -50 * b2.mV
Vreset = -70 * b2.mV
R = 10 * b2.Mohm
eqs_lif = """
dV/dt = (-(V - Vr) + R*I) / tau : volt
I : amp
"""
G_lif = b2.NeuronGroup(1 , eqs_lif,
threshold="V >= Vt" ,
reset="V = Vreset" ,
method="exact" ,
namespace={"tau" : tau, "Vr" : Vr, "Vt" : Vt, "R" : R, "Vreset" : Vreset})
G_lif.V = Vr
M_lif = b2.StateMonitor(G_lif, ["V" ], record=True )
S_lif = b2.SpikeMonitor(G_lif)
@b2.network_operation(dt=b2.defaultclock.dt )
def update_current ():
t = b2.defaultclock.t
G_lif.I = 2.5 * b2.nA if t > 100 * b2.ms else 0 * b2.nA
net = b2.Network(G_lif, M_lif, S_lif, update_current)
net.run(500 * b2.ms)
print (f"LIF neuron fired {S_lif.num_spikes} times" )
print (f"Firing rate: {S_lif.num_spikes / 0.4 :.1 f} Hz (during stimulus)" )
fig, ax = plt.subplots(figsize=(10 , 3 ))
ax.plot(M_lif.t / b2.ms, M_lif.V[0 ] / b2.mV, 'b-' , linewidth=0.8 )
ax.axvline(100 , color='r' , linestyle='--' , label='Stimulus onset' )
for t_sp in S_lif.t / b2.ms:
ax.axvline(t_sp, color='k' , alpha=0.5 , linewidth=0.5 )
ax.set_xlabel("Time (ms)" ); ax.set_ylabel("V (mV)" )
ax.set_title(f"LIF Neuron — {S_lif.num_spikes} spikes" )
ax.legend()
plt.tight_layout()
plt.savefig("lif_neuron.png" , dpi=150 )
plt.show()
Step 2: Recurrent E-I Network import brian2 as b2
import numpy as np
import matplotlib.pyplot as plt
b2.start_scope()
b2.defaultclock.dt = 0.1 * b2.ms
N_E = 400
N_I = 100
tau_E, tau_I = 20 *b2.ms, 10 *b2.ms
V_rest = -70 *b2.mV
V_thresh = -50 *b2.mV
V_reset = -60 *b2.mV
tau_ref = 2 *b2.ms
eqs = """
dV/dt = (-(V - V_rest) + I_ext + I_syn) / tau : volt (unless refractory)
I_ext : volt
I_syn : volt
"""
P_E = b2.NeuronGroup(N_E, eqs,
threshold="V >= V_thresh" , reset="V = V_reset" ,
refractory=tau_ref, method="euler" ,
namespace={"V_rest" : V_rest, "V_thresh" : V_thresh,
"V_reset" : V_reset, "tau" : tau_E})
P_I = b2.NeuronGroup(N_I, eqs,
threshold="V >= V_thresh" , reset="V = V_reset" ,
refractory=tau_ref, method="euler" ,
namespace={"V_rest" : V_rest, "V_thresh" : V_thresh,
"V_reset" : V_reset, "tau" : tau_I})
P_E.V = V_rest + b2.rand(N_E) * 10 * b2.mV
P_I.V = V_rest + b2.rand(N_I) * 10 * b2.mV
P_E.I_ext = 5 * b2.mV
S_EE = b2.Synapses(P_E, P_E, on_pre="I_syn += 0.5*mV" , delay=1 *b2.ms)
S_EI = b2.Synapses(P_E, P_I, on_pre="I_syn += 1.0*mV" , delay=1 *b2.ms)
S_IE = b2.Synapses(P_I, P_E, on_pre="I_syn -= 2.0*mV" , delay=1 *b2.ms)
S_EE.connect(p=0.05 , condition="i != j" )
S_EI.connect(p=0.10 )
S_IE.connect(p=0.25 )
sp_E = b2.SpikeMonitor(P_E)
sp_I = b2.SpikeMonitor(P_I)
rate_E = b2.PopulationRateMonitor(P_E)
net = b2.Network(P_E, P_I, S_EE, S_EI, S_IE, sp_E, sp_I, rate_E)
net.run(500 * b2.ms)
fig, axes = plt.subplots(2 , 1 , figsize=(10 , 6 ), sharex=True )
axes[0 ].plot(sp_E.t/b2.ms, sp_E.i, 'k.' , ms=1 , alpha=0.5 , label="Excitatory" )
axes[0 ].plot(sp_I.t/b2.ms, sp_I.i + N_E, 'r.' , ms=1 , alpha=0.5 , label="Inhibitory" )
axes[0 ].axhline(N_E, color='r' , linestyle='--' , linewidth=0.5 )
axes[0 ].set_ylabel("Neuron index" )
axes[0 ].set_title(f"E-I Network: {N_E} E + {N_I} I neurons" )
axes[0 ].legend(markerscale=5 )
rate_smooth = b2.PopulationRateMonitor(P_E)
t = rate_E.t / b2.ms
rate_Hz = rate_E.smooth_rate("gaussian" , width=20 *b2.ms) / b2.Hz
axes[1 ].plot(t, rate_Hz, 'b-' )
axes[1 ].set_xlabel("Time (ms)" ); axes[1 ].set_ylabel("Rate (Hz)" )
axes[1 ].set_title("Population Firing Rate (E)" )
plt.tight_layout()
plt.savefig("ei_network.png" , dpi=150 )
plt.show()
print (f"Mean E rate: {rate_Hz[rate_Hz > 0 ].mean():.1 f} Hz" )
Step 3: STDP Synaptic Plasticity import brian2 as b2
import numpy as np
import matplotlib.pyplot as plt
b2.start_scope()
N = 100
tau_pre = 20 * b2.ms
tau_post = 20 * b2.ms
A_plus = 0.01
A_minus = 0.0105
w_max = 1.0
w_init = 0.5
stdp_eqs = """
w : 1
dA_pre/dt = -A_pre / tau_pre : 1 (event-driven)
dA_post/dt = -A_post / tau_post : 1 (event-driven)
"""
pre_on = """
A_pre += {A_plus}
w = clip(w + A_post * {A_minus}, 0, {w_max})
v_post += w
""" .format (A_plus=A_plus, A_minus=A_minus, w_max=w_max)
post_on = """
A_post += {A_minus}
w = clip(w + A_pre * {A_plus}, 0, {w_max})
""" .format (A_minus=A_minus, A_plus=A_plus)
G_pre = b2.PoissonGroup(N, rates=20 *b2.Hz)
G_post = b2.NeuronGroup(N, "dv/dt = -v/(10*ms) : 1" ,
threshold="v > 1" , reset="v = 0" , method="euler" )
syn = b2.Synapses(G_pre, G_post, model=stdp_eqs,
on_pre=pre_on, on_post=post_on)
syn.connect(j="i" )
syn.w = w_init
W_monitor = b2.StateMonitor(syn, "w" , record=range (min (20 , N)))
b2.run(5 * b2.second)
fig, axes = plt.subplots(1 , 2 , figsize=(10 , 4 ))
final_weights = syn.w[:]
axes[0 ].hist(final_weights, bins=20 , color="steelblue" , edgecolor="white" )
axes[0 ].axvline(w_init, color='r' , linestyle='--' , label=f"Initial w={w_init} " )
axes[0 ].set_xlabel("Synaptic weight" ); axes[0 ].set_ylabel("Count" )
axes[0 ].set_title("Weight Distribution After STDP" ); axes[0 ].legend()
for i in range (min (5 , len (W_monitor.t))):
axes[1 ].plot(W_monitor.t/b2.second, W_monitor.w[i], lw=0.8 , alpha=0.8 )
axes[1 ].set_xlabel("Time (s)" ); axes[1 ].set_ylabel("Weight" )
axes[1 ].set_title("Weight Trajectories (5 synapses)" )
plt.tight_layout()
plt.savefig("stdp_weights.png" , dpi=150 )
plt.show()
print (f"Initial mean weight: {w_init:.3 f} " )
print (f"Final mean weight: {final_weights.mean():.3 f} " )
print (f"Final std weight: {final_weights.std():.3 f} " )
Advanced Usage
Hodgkin-Huxley Conductance Model import brian2 as b2
import numpy as np
import matplotlib.pyplot as plt
b2.start_scope()
hh_eqs = """
dV/dt = (I_ext - gNa*m**3*h*(V-ENa) - gK*n**4*(V-EK) - gL*(V-EL)) / Cm : volt
dm/dt = alpham*(1-m) - betam*m : 1
dh/dt = alphah*(1-h) - betah*h : 1
dn/dt = alphan*(1-n) - betan*n : 1
alpham = (0.1/mV) * (-V - 40*mV) / (exp((-V - 40*mV)/(10*mV)) - 1)/ms : Hz
betam = 4 * exp((-V - 65*mV)/(18*mV))/ms : Hz
alphah = 0.07 * exp((-V - 65*mV)/(20*mV))/ms : Hz
betah = 1 / (exp((-V - 35*mV)/(10*mV)) + 1)/ms : Hz
alphan = (0.01/mV)*(-V - 55*mV) / (exp((-V-55*mV)/(10*mV)) - 1)/ms : Hz
betan = 0.125 * exp((-V - 65*mV)/(80*mV))/ms : Hz
I_ext : amp/metre**2
"""
params = dict (gNa=120 *b2.msiemens/b2.cm**2 , gK=36 *b2.msiemens/b2.cm**2 ,
gL=0.3 *b2.msiemens/b2.cm**2 , ENa=50 *b2.mV, EK=-77 *b2.mV,
EL=-54.4 *b2.mV, Cm=1 *b2.ufarad/b2.cm**2 )
G_hh = b2.NeuronGroup(1 , hh_eqs, method="exponential_euler" , namespace=params)
G_hh.V = -65 * b2.mV
G_hh.m = 0.05 ; G_hh.h = 0.6 ; G_hh.n = 0.32
G_hh.I_ext = 10 * b2.uamp / b2.cm**2
M_hh = b2.StateMonitor(G_hh, ["V" , "m" , "h" , "n" ], record=True )
sp_hh = b2.SpikeMonitor(G_hh)
b2.run(100 * b2.ms)
fig, axes = plt.subplots(2 , 1 , figsize=(10 , 6 ), sharex=True )
axes[0 ].plot(M_hh.t/b2.ms, M_hh.V[0 ]/b2.mV, 'k-' , linewidth=1.2 )
axes[0 ].set_ylabel("V (mV)" ); axes[0 ].set_title("Hodgkin-Huxley Neuron" )
for var, color in zip (["m" , "h" , "n" ], ["b" , "r" , "g" ]):
axes[1 ].plot(M_hh.t/b2.ms, getattr (M_hh, var)[0 ], color=color, label=var, lw=1.2 )
axes[1 ].set_xlabel("Time (ms)" ); axes[1 ].set_ylabel("Gating variable" )
axes[1 ].legend()
plt.tight_layout()
plt.savefig("hodgkin_huxley.png" , dpi=150 )
plt.show()
print (f"HH spikes: {sp_hh.num_spikes} " )
Troubleshooting
Error: BrianObjectException: Variable ... is not defined Cause : Namespace mismatch between equation string and Python scope.
G = b2.NeuronGroup(N, eqs, namespace={"tau" : tau, "Vr" : Vr, "Vt" : Vt})
Issue: Simulation too slow for large networks
b2.set_device("cpp_standalone" , directory="output" )
b2.run(...)
Version Compatibility Package Tested versions Known issues brian2 2.5, 2.6, 2.7 Equation syntax stable since 2.4
External Resources
Official Documentation
Key Papers
Stimberg, M. et al. (2019). Brian 2, an intuitive and efficient neural simulator . eLife.
Examples
Example 1: Gamma Oscillations in E-I Network
import brian2 as b2
import numpy as np, matplotlib.pyplot as plt
from scipy.signal import welch
b2.start_scope()
b2.defaultclock.dt = 0.05 * b2.ms
N_E, N_I = 800 , 200
eqs_simple = """
dv/dt = (-v + I_net) / tau : 1
I_net : 1
"""
P_E = b2.NeuronGroup(N_E, eqs_simple, threshold="v>1" , reset="v=0" ,
method="euler" , namespace={"tau" : 10 *b2.ms})
P_I = b2.NeuronGroup(N_I, eqs_simple, threshold="v>1" , reset="v=0" ,
method="euler" , namespace={"tau" : 5 *b2.ms})
P_E.v = "rand()" ; P_I.v = "rand()"
P_E.I_net = 1.2 ; P_I.I_net = 1.0
S_EI = b2.Synapses(P_E, P_I, on_pre="I_net += 0.05" , delay=1 *b2.ms)
S_IE = b2.Synapses(P_I, P_E, on_pre="I_net -= 0.2" , delay=2 *b2.ms)
S_EI.connect(p=0.1 ); S_IE.connect(p=0.3 )
rate_mon = b2.PopulationRateMonitor(P_E)
b2.run(500 *b2.ms)
rate = rate_mon.smooth_rate("gaussian" , width=5 *b2.ms) / b2.Hz
t = rate_mon.t / b2.ms
f, Pxx = welch(rate[len (rate)//2 :], fs=1000 /0.1 , nperseg=512 )
peak_freq = f[np.argmax(Pxx)]
print (f"Peak oscillation frequency: {peak_freq:.1 f} Hz" )
fig, axes = plt.subplots(1 , 2 , figsize=(12 , 4 ))
axes[0 ].plot(t, rate, 'b-' , lw=0.8 )
axes[0 ].set_xlabel("Time (ms)" ); axes[0 ].set_ylabel("Rate (Hz)" )
axes[0 ].set_title("Population Rate" )
axes[1 ].semilogy(f[:100 ], Pxx[:100 ], 'r-' )
axes[1 ].axvline(peak_freq, linestyle='--' , label=f"Peak: {peak_freq:.0 f} Hz" )
axes[1 ].set_xlabel("Frequency (Hz)" ); axes[1 ].set_ylabel("PSD" )
axes[1 ].set_title("Power Spectrum" ); axes[1 ].legend()
plt.tight_layout()
plt.savefig("gamma_oscillations.png" , dpi=150 )
plt.show()
Interpreting these results : Peak in the 30-80 Hz range indicates gamma-band synchrony, a hallmark of E-I balanced networks.
Last updated: 2026-03-17 | Maintainer: @xjtulyc
Issues: GitHub Issues