Nootropics vs. Cognitive enhancement Giurgea's nootropic criteria:

Prevent    Maintain    Enhance

Nootropics vs. cognitive enhancers

Cognitive enhancers are drugs, supplements, nutraceuticals, and functional foods that enhance attentional control and memory.^[5][6] Nootropics are cognitive enhancers that are neuroprotective or extremely nontoxic. Nootropics (such as Modafinil) are by definition cognitive enhancers, but a cognitive enhancer is not necessarily a nootropic.
Giurgea's nootropic criteria:

1. Enhances learning and memory.
2. Enhances learned behaviors under conditions which are known to disrupt them (e.g. hypoxia, sleep deprivation).
3. Protects the brain from physical or chemical injury.
4. Enhances the tonic cortical/subcortical control mechanisms
5. Exhibits few side effects and extremely low toxicity, while lacking the pharmacology of typical psychotropic drugs (motor stimulation, sedation, etc.).

Since Giurgea's original criteria were first published, there has been little agreement as to what truly constitutes a nootropic compound. The most well defined criteria to date was established by Skondia in 1979. Skondia uses a metabolic approach, taking into account the pharmacological mode of action.
Skondia's nootropic criteria:
I. No direct vasoactivity

A. No vasodilation

B. No vasoconstriction

II. EEG activity: No change in basic rhythm

A. Quantitative EEG: Increased power spectrum (beta 2 and alpha)

B. Qualitative EEG: Decreased delta waves and cerebral suffering

III. Must pass blood-brain barrier

A. Under normal conditions

B. Under pathological conditions

IV. Must show metabolic activity in:

A. Animal brain metabolism

1. Molecular

2. Physiopathological

B. Human brain metabolism (clinical evaluation)

1. A-V differences

a. Increased extraction quotients of O2

b. Increased extraction quotients of glucose

c. Reduced lactate pyruvate ratio

2. Regional cerebral metabolic rates (rCMR)

a. Increased ICMR of O2

b. Increased rCMR of glucose

3. Regional cerebral blood flow: Normalization

V. Minimal side effects
VI. Clinical trials must be conducted with several rating scales designed to objectify metabolic cerebral improvement.