Composing verses on the fly in an incessant fashion and recalling them at will (dhārā and dhāraṇā) are two important aspects of Avadhānam. In Avadhānam, if impromptu poetry is Śiva, memory is Śakti. The former is forever crippled without the latter.
Not the past, not the future, but the present is the playground of experience. Memory is always related to the past and is the storehouse of knowledge gained by experience. The Sanskrit word for memory is smṛti, which is derived from the root smṛ–ādhyāne / cintāyām. According to this, memory has two defining traits: recollection and thinking. Although memory is an indivisible unit, we may, for the sake of analysis, identify a few steps in its process. It includes not letting a concept slip into oblivion, constantly analysing it from various logical standpoints, and endearingly holding on to it. Dhāraṇā is but a subset of memory because the word primarily means “accommodation” and “encompassment,” which are characteristics of memory. While memory is just the faculty by which we recall, pratibhā is a broader concept that includes its creative application. Bhaṭṭa-tauta famously remarked:
बुद्धिस्तात्कालिकी ज्ञेया प्रज्ञा त्रैकालिकी मता॥
प्रज्ञा नवनवोन्मेषशालिनी प्रतिभा मता।
When the mind can fathom all facts without temporal limitations—i.e., encompassing the past, present, and future—it is termed prajñā. Prajñā transforms into pratibhā (creative imagination) when it can visualize things anew every time it is invoked. A person blessed with creative imagination is a poet and his work is poetry.
Memory should always assist the intellect; otherwise, intellect would be bereft of the experiential input that is essential for its proper functioning. In this light the Bhagavad-gītā (2.63) remarks: “An injury to remembered wisdom impairs the intellect.” What might be the reason for faulty memory? Kṛṣṇa tells us it is delusion—a non-equanimous state of mind propelled by personal likes and dislikes. Therefore, in order to have unruffled wisdom, and by extension impeccable memory, mental composure is a must.
Memory is the abode of everything that comes under the ambit of our emotional and intellectual experience. Fancy finds no place in it. Memory is closely related to medhā, the faculty that retains the kernels of information gained through reading, interacting with the learned, and so on. Retention comes under the purview of memory, and hence medhā can be thought of as a harmonious amalgamation of memory and intellect.
Vidyā-dhara does a fine job of analysing the genesis of memory. It is instructive to look at what he has to say:
Our sense organs collect characteristics of objects and thereby reveal to us their nature. Later, our innate predisposition (saṃskāra) processes and retains this object-oriented knowledge. In due course of time, the retained knowledge manifests itself as memory.
Memory as Understood by Indian Thinkers
Various schools of Indian philosophy are replete with invaluable discussions about memory. While the Nyāya school does not count it as a means to validate knowledge, the Vaiśeṣika school regards it as a subset of saṃskāra, one of the twenty-four guṇas that it advocates (ref: ‘bhāvanā’). The Sāṅkhya system refers to it as a feature that assists vṛtti, the cognitive process. According to Yoga, memory is one of the spokes of the vṛtti-saṃskāra-cakra, the wheel of cognition. The Yoga school also identifies strong memory as prajñā. The Mīmāṃsā school recognizes memory as an authentic tool to validate knowledge and slots it under dharma. In a similar fashion, Vedānta identifies memory as a subservient entity of cognition, and at times relates it to codanā, the faculty that stimulates activity. The Lokāyata system counts it in connection with direct perception. The Jaina system accommodates it under mati, one of the kinds of indirect perception. According to the Bauddha school, memory is related to three among the five ways in which distress can manifest: rūpa (form), vijñāna (imagination), and sañjñā (name). Buddhism further enlists twelve reasons for distress (dvādaśa-nidānas), which include name, form, and imagination.
The Yoga system enumerates memory and retention in greater detail when compared to other schools of Indian philosophy. The reason for this lies in the practice-oriented nature of Yoga, whose cardinal objective is to control the mind (citta) and its activities (vṛtti). Almost all words in Sanskrit that are synonymous with ‘mind’ are coloured by the influence of Yoga. The Vaidika tradition avers that it is possible to sharpen the edge of memory by controlling mind, body, and speech.
Yoga-sūtras describe memory as anubhūta-viṣayāsampramoṣaḥ (1.11). Accordingly, memory is retaining experienced objects in the mind through saṃskāra. The commentary of Vyāsa thereon describes mind as the seat of retention, and memory as that which is to be retained. It then proceeds to elucidate two kinds of memory that are related to realistic and unrealistic objects of experience: abhāvita-smartavya and bhāvita-smartavya. It also relates the memory of the dream state to bhāvita-smartavya and that of the wakeful state to abhāvita-smartavya.
While discussing dhāraṇā, the Yoga-sūtras say deśa-bandhaścittasya dhāraṇā (3.1). Accordingly, focusing the mind on a single point is the prime requisite of retention. Among the eight limbs of Yoga, the first five (yama, niyama, āsana, prāṇāyāma, and pratyāhāra) roughly relate to external features, and the last three (dhāraṇā, dhyāna, and samādhi) relate to internal ones. The Yoga-sudhākara commentary of Sadāśiva-brahmendra quotes a verse from Yoga-yājñavalkya-smṛti, which says retention is that state of the mind that is refined by yama, niyama, āsana, prāṇāyāma, and pratyāhāra.
Tattva-vaiśāradī gloss on Vyāsa’s commentary quotes a line from Viṣṇu-purāṇa. Retention, in this light, is the process of making the mind firm. Yet another Yoga-sūtra declares that breath-control (prāṇāyāma) ensures strong retention. In this way, the Yoga school discusses in detail various aspects of memory and retention.
Vallabha-deva, one of the many commentators of Raghu-vaṃśa, lists various functions of the intellect:
Desire to listen, listening itself, grasping the meaning, retention, inferring desirable details, jettisoning unwanted details, contemplating on the import, and comprehensive understanding are the functions of the intellect. 
Retention occupies the central position amongst these. It bridges listening and comprehension. Seen this way, memory is not an independent entity; it is the nodal point of numerous functions.
Yaśodhara’s commentary on Kāma-sūtras presents an interesting and most agreeable picture of memory. It does so while dealing with the sixty-four arts, among which dhāraṇā-mātṛkā is one: 
The topic to be known, words and their meanings, contextual knowledge, unique features of the topic, and logical reasoning constitute the beautiful body of the deity of retention.
Vastu, Koṣa, Dravya, Lakṣaṇa, and Hetu are accordingly the five features that constitute retention. We can understand this better through an example.
Let us consider a verse composed by Panḍīta-rāja Jagannātha and identify the five features enlisted above:
तीरे तरुण्या वदनं सहासं
नीरे सरोजं च मिलद्विकासम्।
आलोक्य धावत्युभयत्र मुग्धा
There is the smiling face of a damsel on the bank and a lotus in full bloom in the pond. Looking at them, a string of young bees, desirous of nectar, runs towards both.
- Vastu: Description of the beauty of a woman’s face.
- Koṣa: A woman’s smiling face, a lotus in full bloom, young bees, and desire for nectar. Rhyming words: tīre, nīre; sahāsaṃ, vikāsam; mugdhā, lubdhā.
- Dravya: A woman’s smiling face is similar to a bloomed lotus.
- Lakṣaṇa: Metre (Upa-jāti); Figures of sound (rhyme and alliteration); Figure of sense (bhrāntimān; confusion).
- Hetu: Jagannātha’s penchant for figures of sound (especially) and sense; his eagerness to describe women’s beauty; lucidity that marks out all his verses.
If one understands all these five elements, he can retain the verse in mind for a long time and recall it at will. Retentive power of this kind comes to the help of a performer during Sāhityāvadhānam.
Although various treatises of Āyurveda discuss a few features of memory, their primary concern lies with medicines that are supposed to enhance memory, and with general healthcare and its impact on memory; they hardly ponder over physiological aspects of memory and retention. Since modern science has a lot to say in this regard, it is appropriate to presently consider those details at some length.
 शिवः शक्त्या युक्तो यदि भवति शक्तः प्रभवितुं न चेदेवं देवो न खलु कुशलः स्पन्दितुमपि। (Saundarya-laharī, verse #1)
 Kāvya-kautukādarśa, p. 36
 धीर्धारणावती मेधा। (Amara-kośa, 1.157); अनेकश्रुतग्रन्थार्थधारणशक्तिर्मेधा। (Sarva-lakṣaṇa-saṅgraha, p. 115)
 मेधृ-सङ्गमे; मेधते अनुभूतं सर्वमस्यामिति मेधा। चिरानुभूतार्थस्मरणशक्तिः, अनुभूतविषयाधिकानवगाहिज्ञानम्, उद्भूतसंस्कारमात्रजन्यं ज्ञानं संस्कारध्वंसेऽतिव्याप्तिवारणाय ज्ञानमिति, प्रत्यभिज्ञायामतिव्याप्तिवारणाय मात्रपदं, अनुभवेऽतिव्याप्तिवारणाय संस्कारजन्यमिति, असम्भववारणायोद्भूतमिति। (Sarva-lakṣaṇa-saṅgraha, p. 163–64)
 वस्तुविषयस्तावदात्मन्यनुभवपूर्वमिन्द्रियसन्निकर्षादिना जन्यते। जनितेन संस्कार आधीयते। आहितेन च तेन कालान्तरे स्मृतिरुत्पद्यते। संस्काराधानद्वारा स्मृतिं प्रत्यनुभवस्य कारणत्वम्। (Ekāvalī, chapter 3, p. 88)
 Ref: Ṣaḍ-darśana-saṅgraha (Kannada)
 बुद्धिर्मनीषा धिषणा धीः प्रज्ञा शेमुषी मतिः। प्रेक्षोपलब्धिश्चित्संवित्प्रतिपज्ज्ञप्तिचेतनाः॥
धीर्धारणावती मेधा सङ्कल्पः कर्म मानसम्। अवधानं समाधानं प्रणिधानं तथैव च॥ (Amara-kośa, 1.156–57)
मनुते मनीषा मनस एवेषा वा। देदेष्टि धिषणा, ध्यायति धीयते वास्यां धीः। शेते मोहस्तं मुष्णाति शेमुषी। (Kṣīra-svāmī’s gloss)
All words that denote knowledge and memory in Sanskrit are derived from roots that suggest dynamism (gatyarthaka-dhātavaḥ). This indicates the intrinsic dynamic nature of memory and knowledge.
 आहारशुद्धौ सत्त्वशुद्धिः। सत्त्वशुद्धौ ध्रुवा स्मृतिः। (Chāndogyopaniṣad, 7.26.2)
आहारशुद्धौ। आह्रियत इत्याहारः शब्दादिविषयविज्ञानं भोक्तुर्भोगायाह्रियते। तस्य विषयोपलब्धिलक्षणस्य विज्ञानस्य शुद्धिराहारशुद्धिः, रागद्वेषमोहदोषैरसंसृष्टं विषयविज्ञानमित्यर्थः। तस्यामाहारशुद्धौ सत्यां तद्वतोऽन्तःकरणस्य सत्त्वस्य शुद्धिर्नैर्मल्यं भवति। सत्त्वशुद्धौ च सत्यां यथावगते भूमात्मनि ध्रुवाविच्छिन्ना स्मृतिरविस्मरणं भवति। (Śaṅkarācārya’s commentary)
This passage gives us extraordinary insight into food and the ways of consuming it: Everything that we take in [through the senses] is āhāra. There must be no trace of personal likes and dislikes in the process of consumption. This is crucial to achieve unfailing memory. Further, an undisturbed process of consumption, coupled with an optimal association with the object to be consumed, leads to sound memory.
A related passage from Mahānārāyaṇopaniṣad (23.1) is worthy of reference:
अन्नेन प्राणाः ... चित्तेन स्मृतिः ... स्मृत्या स्मारम् ... स्मारेण विज्ञानम् ... विज्ञानेनात्मानं वेदयति।
According to this, memory is the binding cord of the four sheaths that make a living being: anna-maya, prāṇa-maya, manomaya, and vijñāna-maya. The Ultimate Self that dwells in the fifth sheath (ānanda-maya) is realized through vijñāna. And it is food (in the broad sense as explained above) that triggers the link between the sheaths.
Hunger disrupts the activities of mind and body. As a result, memory is affected. This is explained in Chāndogyopaniṣad (6.7.1–6) in connection with Śveta-ketu.
 यमादिगुणयुक्तस्य मनसः स्थितिरात्मनि।
 एषा वै धारणा ज्ञेया यच्चित्तं तत्र धार्यते। (Viṣṇu-purāṇa, 6.7.77)
 धारणासु च योग्यता मनसः। (Yoga-sūtra, 2.53)
 शुश्रूषा श्रवणं चैव ग्रहणं धारणं तथा।
ऊहापोहोऽर्थविज्ञानं तत्त्वज्ञानं च धीगुणाः॥ (Vallabha-deva’s commentary on Raghu-vaṃśa, 3.30)
 वस्तु कोषस्तथा द्रव्यं लक्षणं हेतुरेव च।
इत्येते धारणादेव्याः पञ्चाङ्गरुचिरं वपुः॥ (Kāma-sūtra, 1.3.16)
 Bhāminī-vilāsa, 2.21
To be continued.