How to show memos without using a mouse

I'm using a DBGrid and a DBMemo. When moving to a cell with a
cursorkey the content should be displayed in the DBMemo if the field
is a Memo-field
Using the mouse is easy like:

procedure TMainForm.DBGrid1CellClick(Column: TColumn);

begin
  if Column.Field is TMemoField then
  begin
    DBMemo1.Datafield := Column.Fieldname;
    DBMemo1.Enabled := True;
    DBMemo1.Visible := True;
  end
end;

but how do I achive the same using only the keyboard ?
Using OnDrawColumnCell shows the memo only after leaving the cell ?!