From a scientific point of view, two of the most interesting aspects of the sounds called mantras are their reported ability to tune the brainwave frequencies, and to stimulate the energy centres called chakras. Firstly, tuning or entrainment of the brainwave frequencies can be achieved with certain specific syllables or sounds, thus creating a change in the overall state of the thought patterns of the mind.
Secondly, there are mantras that activate the specific energies associated with the chakras, which are the bodily complexes associated with individual primary aspects of the mind. This is principally achieved via a number of specialized sounds called the bija mantras of the chakras: lam, vam, ram, yam, ham, aum. This is a process we might call 'archetypal harmony', as it involves keying into something elemental in the mind at a very specific level.
The first major aspect of mantra is the ability of specific sounds to alter the predominant brainwave frequency. To experience a calm but aware inner state, one needs to bring the brainwave frequency to about ten cycles per second the 'alpha' state. If the frequency is too high, our awareness tends to be either externalized, or caught up in a torrent of active thoughts. If the frequency is too low, we move into an unconscious state. It is important to maintain an alpha state for effective meditation practice, so that we can become more aware and accepting of our nature. A simple way to achieve this is via the mantra Aum. This consists of three syllables, each with a specific effect:
The combination of these sounds, repeated with appropriate durations for each syllable, can tune the brainwaves to alpha (10Hz), which creates a relaxed, creative awareness and sometimes a very blissful state of mind. An effective way to practise Aum is to set the ratio of the durations of the syllables to one for 'a', one for 'u' and four for 'mmmm' and repeat the sound for about ten minutes while sitting very still.
The chakras are known as psychic centres. They are located at points in the physical body where there is direct interaction between the energies of a specific 'room' or department of the mind and the physical body. Physically the interaction takes place via the dual media of the nervous system and the endocrine glands. The various departments of the mind, in this sense, are related to different levels and regions of expression and perception.
Beyond there is sahasrara, at the crown of the head, associated with our personal spiritual connection to the absolute.
For each of the chakras, as an aspect of mind, there is a large range of images, sounds and melodies which will create activity or stimulation of that region. In their most essential or archetypal form the images are known as yantras (specific geometric shapes) and the sounds are known as mantras. The effect of sounds is dependent on their pitch, rhythm and syllabic structure. The results of stimulation of a centre may be on the level of evoking a feeling, an image (a scene or shape), a sound may be heard, or there may be a manifestation of a situation in life connected with that chakra.
Each centre is a powerhouse of some complexity and many experiences manifest when a chakra becomes more active. Activation of the centres is a normal and necessary state in our lives, but it often happens in a haphazard fashion with lots of complications. But gentle and systematic stimulation of the chakras can be achieved via various yoga practices, especially mantra. Such gentle stimulation allows our abilities and effectiveness as human beings to increase without creating an overload or imbalance.
As mentioned above, some specific sounds, which are keys to stimulating the chakras, are called the bija mantras of the chakras. One group of bija mantras are: Lam (pronounced lum) for mooladhara; Vam (pronounced vum) for swadhisthana; Ram (pronounced rum) for manipura; Yam (pronounced yum) for anahata; Ham (pronounced hum) for vishuddhi; Aum (pronounced om) for ajna.
A good practice for balanced stimulation is to mentally repeat the mantras while taking the awareness to the relevant chakra. This should be done in order, while breathing in, starting from mooladhara (lam) and moving one by one to vishuddhi (ham). In this way we do each mantra once (lam, vam, ram, yam, ham) during inhalation of the breath up to the throat. Then we pronounce the extended sound Aum breathing out, with the awareness starting at ajna (eyebrow centre) and descending during exhalation right back to mooladhara, where we begin the cycle again with lam (mentally). For initial familiarization we can pronounce the mantras out loud, each on one breath, with the awareness at the relevant chakra.
Awakening of the chakra energies is awakening of parts of our nature. To deal with the positive nature is easy, but to deal with the negative nature can be very difficult. It is often necessary to seek advice from a competent teacher or guide (guru).
There is a further range of more sophisticated mantras based on the sounds of the Sanskrit language (and some from other languages such as Greek, Latin and Hebrew). These may be quite long phrases, such as Aum Namah Shivayah. In each case they key directly into a particular set of archetypes in the elementary nature of the human consciousness, and each one awakens a certain aspect of our makeup. Their literal meaning or translation is not important. There are many mantras that are suitable for general usage, such as the Gayatri: Om bhur bhuvah svaha tat savitur varenyam, bhargo devasya dheemahi, dhiyo yo nah prachodayaat. These are generally chanted to an even rhythm.
For each individual, depending on the personality, certain mantras are more appropriate, and the choice of which to use is difficult for the beginner. For such a personal mantra one should seek the advice of an expert the guru.
When mantras are combined with musical melodies the result is one of the most effective forms of yoga kirtan. The introduction of music and rhythm keys into the emotional aspect of our being, producing a wonderful sense of completeness and relaxation.
This is a very brief overview of mantra. Nearly all the knowledge we have on this subject has been derived from the ancient yogic tradition. Much research remains to be done to provide thorough statistics about the effectiveness of mantra. Yet the anecdotal evidence from those who practise any one of the techniques of mantra is that it does help a great deal in achieving better health as well as a more positive and creative frame of mind.