The sense organ of the sixth consciousness includes a mental component and a physical component. The mental component is the retribution consciousness. It arises from the eighth consciousness where the karmic seeds reside. However, without the physical component, the karmic seeds cannot manifest. The physical component functions like a doorway, allowing the retribution consciousness ─ past karma ─ to leave the karmic storehouse and allowing newly created karma to enter the karmic storehouse. The physical component is one's nervous system.

STUDENT:

Then the mental function of the sixth consciousness incorporates the other five sense organs? Isn't it the brain and nervous system that senses, perceives and processes all information?

SHIH-FU:

Yes, but when I speak of the sixth consciousness I am talking about that part of the brain associated with thinking, reasoning and memory. The nervous system also includes the other sense consciousnesses and the life functions, but they are not part of the sense organ of the sixth consciousness. The brain and nervous system have more than one function.

In order for a sentient being to reason or have memory, it must make use of symbols. It is questionable how much memory and reasoning power other animals have. As long as an organism has a nervous system, then it still has the first four skandhas: form, sensation, perception and volition. Without the first four skandhas a sentient being would not be able to function; but only sentient beings with memory and reasoning power (those that make use of symbols) have all five skandhas.

STUDENT:

What about plants and vegetables? They seem to respond to things. They grow toward light.