Assigning events to the mouse wheel
It’s possible to assign events to the mouse wheel in GIMP. For example you can use the mouse wheel to change the brushes’ size.
In order to do this go to the Edit menu-Preferences-Input Devices-Input Controllers, select «Main Mouse Wheel» and make it active through moving to the right pane.
Then double-click on it and you will see the Configure Input Controller window. There are no actions opposite the Scroll Up and Scroll Down events.
Double-click the Scroll Up event and select action Context-Increase Radius More. Do the same with the Scroll Down event but select Context-Decrease Radius More.