Result of "echo df":

Dataframe with 2 columns and 28 rows:
        Idx     spikes    neurons
     dtype:        int        int
          0          0          0
          1        502          0
          2        502          0
          3        502          0
          4        502          0
          5        502          0
          6        502          0
          7        502          0
          8        502          0
          9        502          0
         10        502          0
         11        502          0
         12        502          0
         13        502          0
         14        502          0
         15        502          0
         16        502          0
         17        502          0
         18        502          0
         19        502          0

Code:

ggplot(df, aes("spikes", "neurons")) +
  geom_linerange(aes(ymin = f{1.0},
                     ymax = f{-1.0})) +
  scale_y_continuous() + # make sure y is considered cont.
  ylim(1, -1) + # at the moment ymin, ymax are not considered for the plot range (that's a bug)
  ggtitle("Spike raster plot") +
  ggsave("spike_raster.pdf")