Figure 2.

Relationship between spike shape and mean frequency: Consider two spikes coming out of an amperometric trace, $s_1$representing a high frequency oscillation (hence a thin spike) and $s_2$ representing a low frequency oscillation (and hence a wide spike). We expect that the wider the curve, the lower is the mean frequency i.e. $f_{\text{mean}}(s_1)>f_{\text{mean}}(s_2)$.