Habilitando o Scroll do Mouse;
ache no Arquivo /etc/X11/XF86Config-4 as linhas:

Section "InputDevice"
Identifier "PS/2 Mouse"
Driver "mouse"
Option "Protocol" "PS/2"
Option "Device" "/dev/psaux"
Option "Emulate3Buttons" "true"
Option "Emulate3Timeout" "70"
Option "SendCoreEvents" "true"
EndSection

mude para:

Section "InputDevice"
Identifier "PS/2 Mouse"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/psaux"
Option "ZAxisMapping" "4 5"
Option "Butons" "5"
Option "Emulate3Buttons" "true"
Option "Emulate3Timeout" "70"
Option "SendCoreEvents" "true"
EndSection