def numberOfProximalSynapses(self, cells=None):
    """
    Returns the number of proximal synapses with permanence>0 on these cells.

    Parameters:
    ----------------------------
    @param  cells (iterable)
            Indices of the cells. If None return count for all cells.
    """
    if cells is None:
      cells = xrange(self.numberOfCells())

    n = 0
    for cell in cells:
      n += self.proximalPermanences.nNonZerosOnRow(cell)
    return n