def _get_neuron_id(dataframe):
    """Unique identifier string for a neuron"""
    return dataframe.animal + '_' + dataframe.day.map('{:02d}'.format
        ) + '_' + dataframe.epoch.map('{:02}'.format
        ) + '_' + dataframe.tetrode_number.map('{:03}'.format
        ) + '_' + dataframe.neuron_number.map('{:03}'.format)
