# Changes for Brian 1 users¶

In most cases, Brian 2 works in a very similar way to Brian 1 but there are some important differences to be aware of. The major distinction is that in Brian 2 you need to be more explicit about the definition of your simulation in order to avoid inadvertent errors. In some cases, you will now get a warning in other even an error – often the error/warning message describes a way to resolve the issue.

Specific examples how to convert code from Brian 1 can be found in the document Detailed Brian 1 to Brian 2 conversion notes.

## Physical units¶

The unit system now extends to arrays, e.g. np.arange(5) * mV will retain the units of volts and not discard them as Brian 1 did. Brian 2 is therefore also more strict in checking the units. For example, if the state variable v uses the unit of volt, the statement G.v = np.rand(len(G)) / 1000. will now raise an error. For consistency, units are returned everywhere, e.g. in monitors. If mon records a state variable v, mon.t will return a time in seconds and mon.v the stored values of v in units of volts.

If you need a pure numpy array without units for further processing, there are several options: if it is a state variable or a recorded variable in a monitor, appending an underscore will refer to the variable values without units, e.g. mon.t_ returns pure floating point values. Alternatively, you can remove units by diving by the unit (e.g. mon.t / second) or by explicitly converting it (np.asarray(mon.t)).

Here’s an overview showing a few expressions and their respective values in Brian 1 and Brian 2:

Expression Brian 1 Brian 2
1 * mV 1.0 * mvolt 1.0 * mvolt
np.array(1) * mV 0.001 1.0 * mvolt
np.array() * mV array([ 0.001]) array([1.]) * mvolt
np.mean(np.arange(5) * mV) 0.002 2.0 * mvolt
np.arange(2) * mV array([ 0. , 0.001]) array([ 0., 1.]) * mvolt
(np.arange(2) * mV) >= 1 * mV array([False, True], dtype=bool) array([False, True], dtype=bool)
(np.arange(2) * mV) >= 1 * mV False False
(np.arange(2) * mV) >= 1 * mV DimensionMismatchError True

## Unported packages¶

The following packages have not (yet) been ported to Brian 1. If your simulation critically depends on them, you should consider staying with Brian 1 for now.

• brian.tools
• brian.hears (the Brian 1 version can be used via brian2.hears, though, see Brian Hears)
• brian.library.modelfitting
• brian.library.electrophysilogy

## Removed classes/functions and their replacements¶

In Brian 2, we have tried to keep the number of classes/functions to a minimum, but make each of them flexible enough to encompass a large number of use cases. A lot of the classes and functions that existed in Brian 1 have therefore been removed. The following table lists (most of) the classes that existed in Brian 1 but do no longer exist in Brian 2. You can consult it when you get a NameError while converting an existing script from Brian 1. The third column links to a document with further explanation and the second column gives either:

1. the equivalent class in Brian 2 (e.g. StateMonitor can record multiple variables now and therefore replaces MultiStateMonitor);
2. the name of a Brian 2 class in square brackets (e.g. [Synapses] for STDP), this means that the class can be used as a replacement but needs some additional code (e.g. explicitly specified STDP equations). The “More details” document should help you in making the necessary changes;
3. “string expression”, if the functionality of a previously existing class can be expressed using the general string expression framework (e.g. threshold=VariableThreshold('Vt', 'V') can be replaced by threshold='V > Vt');
4. a link to the relevant github issue if no equivalent class/function does exist so far in Brian 2;
5. a remark such as “obsolete” if the particular class/function is no longer needed.
Brian 1 Brian 2 More details
AdEx [Equations] Library models (Brian 1 –> 2 conversion)
aEIF [Equations] Library models (Brian 1 –> 2 conversion)
AERSpikeMonitor #298 Monitors (Brian 1 –> 2 conversion)
alpha_conductance [Equations] Library models (Brian 1 –> 2 conversion)
alpha_current [Equations] Library models (Brian 1 –> 2 conversion)
alpha_synapse [Equations] Library models (Brian 1 –> 2 conversion)
AutoCorrelogram [SpikeMonitor] Monitors (Brian 1 –> 2 conversion)
biexpr_conductance [Equations] Library models (Brian 1 –> 2 conversion)
biexpr_current [Equations] Library models (Brian 1 –> 2 conversion)
biexpr_synapse [Equations] Library models (Brian 1 –> 2 conversion)
Brette_Gerstner [Equations] Library models (Brian 1 –> 2 conversion)
CoincidenceCounter [SpikeMonitor] Monitors (Brian 1 –> 2 conversion)
CoincidenceMatrixCounter [SpikeMonitor] Monitors (Brian 1 –> 2 conversion)
Compartments #443 Multicompartmental models (Brian 1 –> 2 conversion)
Connection Synapses Synapses (Brian 1 –> 2 conversion)
Current #443 Multicompartmental models (Brian 1 –> 2 conversion)
CustomRefractoriness [string expression] Neural models (Brian 1 –> 2 conversion)
DefaultClock Clock Networks and clocks (Brian 1 –> 2 conversion)
EmpiricalThreshold string expression Neural models (Brian 1 –> 2 conversion)
EventClock Clock Networks and clocks (Brian 1 –> 2 conversion)
exp_conductance [Equations] Library models (Brian 1 –> 2 conversion)
exp_current [Equations] Library models (Brian 1 –> 2 conversion)
exp_IF [Equations] Library models (Brian 1 –> 2 conversion)
exp_synapse [Equations] Library models (Brian 1 –> 2 conversion)
FileSpikeMonitor #298 Monitors (Brian 1 –> 2 conversion)
FloatClock Clock Networks and clocks (Brian 1 –> 2 conversion)
FunReset [string expression] Neural models (Brian 1 –> 2 conversion)
FunThreshold [string expression] Neural models (Brian 1 –> 2 conversion)
hist_plot no equivalent
HomogeneousPoissonThreshold string expression Neural models (Brian 1 –> 2 conversion)
IdentityConnection Synapses Synapses (Brian 1 –> 2 conversion)
IonicCurrent #443 Multicompartmental models (Brian 1 –> 2 conversion)
ISIHistogramMonitor [SpikeMonitor] Monitors (Brian 1 –> 2 conversion)
Izhikevich [Equations] Library models (Brian 1 –> 2 conversion)
K_current_HH [Equations] Library models (Brian 1 –> 2 conversion)
leak_current [Equations] Library models (Brian 1 –> 2 conversion)
leaky_IF [Equations] Library models (Brian 1 –> 2 conversion)
MembraneEquation #443 Multicompartmental models (Brian 1 –> 2 conversion)
MultiStateMonitor StateMonitor Monitors (Brian 1 –> 2 conversion)
Na_current_HH [Equations] Library models (Brian 1 –> 2 conversion)
NaiveClock Clock Networks and clocks (Brian 1 –> 2 conversion)
NoReset obsolete Neural models (Brian 1 –> 2 conversion)
NoThreshold obsolete Neural models (Brian 1 –> 2 conversion)
OfflinePoissonGroup [SpikeGeneratorGroup] Inputs (Brian 1 –> 2 conversion)
OrnsteinUhlenbeck [Equations] Library models (Brian 1 –> 2 conversion)
perfect_IF [Equations] Library models (Brian 1 –> 2 conversion)
PoissonThreshold string expression Neural models (Brian 1 –> 2 conversion)
PopulationSpikeCounter SpikeMonitor Monitors (Brian 1 –> 2 conversion)
PulsePacket [SpikeGeneratorGroup] Inputs (Brian 1 –> 2 conversion)
quadratic_IF [Equations] Library models (Brian 1 –> 2 conversion)
raster_plot plot_raster (brian2tools) brian2tools documentation
RecentStateMonitor no direct equivalent Monitors (Brian 1 –> 2 conversion)
Refractoriness string expression Neural models (Brian 1 –> 2 conversion)
RegularClock Clock Networks and clocks (Brian 1 –> 2 conversion)
Reset string expression Neural models (Brian 1 –> 2 conversion)
SimpleCustomRefractoriness [string expression] Neural models (Brian 1 –> 2 conversion)
SimpleFunThreshold [string expression] Neural models (Brian 1 –> 2 conversion)
SpikeCounter SpikeMonitor Monitors (Brian 1 –> 2 conversion)
StateHistogramMonitor [StateMonitor] Monitors (Brian 1 –> 2 conversion)
StateSpikeMonitor SpikeMonitor Monitors (Brian 1 –> 2 conversion)
STDP [Synapses] Synapses (Brian 1 –> 2 conversion)
STP [Synapses] Synapses (Brian 1 –> 2 conversion)
StringReset string expression Neural models (Brian 1 –> 2 conversion)
StringThreshold string expression Neural models (Brian 1 –> 2 conversion)
Threshold string expression Neural models (Brian 1 –> 2 conversion)
VanRossumMetric [SpikeMonitor] Monitors (Brian 1 –> 2 conversion)
VariableReset string expression Neural models (Brian 1 –> 2 conversion)
VariableThreshold string expression Neural models (Brian 1 –> 2 conversion)