We can use SSI_CustomGraphicalCheckbox to know when a checkbox is checked or unchecked then use SSI_SetSelect to set the checkbox values as necessary:
<script>
function SSI_CustomGraphicalCheckbox(graphicalObj, inputObj, bln) {
var match = inputObj.name.match(/Q9_va_([0-9]+)/);
if (match !== null && bln) {
if (Number(match[1]) == 22) {
for (var i = 1; i <= 21; i++) {
SSI_SetSelect('Q9_va_' + i, false);
}
}
else {
SSI_SetSelect('Q9_va_22', false);
}
}
}
</script>