You want to use the function "minmax". You can see an example of a script that uses this by choosing the Scripting/Templates/basic menu item. You can see a list of all functions with comments regarding their usage by choosing the Scripting/Templates/help menu items. I would use the 'mni152' if you images are the shape of the MNI brain, and spm152 if SPM was used to warp images to the size of an average sized brain (which is smaller than the MNI template).


import gl
gl.resetdefaults()
gl.loadimage('mni152')
gl.opacity(0,70)
gl.backcolor (0, 0, 0)
gl.overlayload('spmMotor')
gl.colorname (1,"6bluegrn")
gl.minmax(1, 4, 4)
gl.colorbarposition(0)
gl.opacity(0,70)