code: def my_callback(ax, ch_idx):
      """Handle axes callback.
  
      This block of code is executed once you click on one of the channel axes
      in the plot. To work with the viz internals, this function should only take
      two parameters, the axis and the channel or data index.
      """
      ax.plot(freqs, psds[ch_idx], color="red")
      ax.set_xlabel("Frequency (Hz)")
      ax.set_ylabel("Power (dB)")
  
imports: import matplotlib.pyplot
  import numpy
  import mne
  from mne import io
  from mne.datasets import sample
  from mne.viz import iter_topography
label_desc: Use image node_id 1 for calling a global function with example usage: my_callback(ax, ch_idx) without return types