When I access the Window/Brushes menu command, the dynamic brush options appeared dimmed. Why is this?

To activate the dynamic brush features ensure that any of the following Brush (Paint) Tools is active from the Toolbar. Brush Tool / Pencil Tool (B), Clone Stamp Tool / Pattern Stamp Tool (S), History Brush Tool / Art History Brush (Y), Eraser Tool (E), Blur Tool / Sharpen Tool / Smudge Tool (R), Dodge / Burn / Sponge (O) Tools