The Neuron Survives, but Its Role Does Not

Confocal images showing the transformation of selected mushroom-body neurons in Drosophila during metamorphosis. The green-labelled neurons are followed through the first 48 hours after pupation as their larval branches retract and new adult connections begin to grow. The cells themselves may survive, while the neural architecture in which they participate is extensively rebuilt. Image adapted from Truman et al., eLife (2023).

Neuron Survives, but Its Role Does Not

Metamorphosis is easy to imagine as a change of form: the larva disappears into the pupa and the adult insect emerges with wings, different senses, different movements, a different way of inhabiting the world. But the transformation reaches much deeper. The nervous system itself is extensively dismantled and rebuilt.

And yet it is not simply replaced.

A remarkable study published in eLife in 2023 followed neurons involved in the mushroom body of Drosophila, a brain structure important for associative learning. The researchers were able to determine the adult fate of 28 of the 32 types of input and output neurons that organize the larval mushroom body. What happened to them was not uniform. Some neurons died. Some survived but shifted into different compartments. Some left the mushroom body altogether and acquired functions in other adult circuits. New adult-specific neurons were recruited into the system.

The most striking result was relational rather than cellular. Although many individual neurons survived metamorphosis, none of the larval connections between the input and output neurons examined in the study remained intact in the adult mushroom-body circuit.

The cells could persist while the relationships that had defined their function disappeared.

The researchers were careful about what this does and does not mean. Their study examined anatomy, not the direct persistence of learned memories. The absence of those particular connections therefore does not prove that nothing learned by a larva can survive metamorphosis. It shows something narrower and, in its own way, stranger: there is no simple preservation of the studied larval circuit through which an associative memory could merely remain where it was.[1]

Earlier experiments suggest that some effects of learning can nevertheless cross this biological rupture. In 2008, Douglas Blackiston, Elena Silva Casey and Martha Weiss trained tobacco hornworm caterpillars (Manduca sexta) to avoid an odour by pairing it with a mild electric shock. Caterpillars trained during their final larval stage retained the aversion after metamorphosis: as adult moths, they continued to avoid the previously conditioned odour. The researchers also tested whether this could simply be caused by chemical traces carried through pupation and found evidence against that explanation.

But the continuity had limits. Caterpillars trained at an earlier developmental stage could retain the learned aversion through subsequent larval moults and yet lose it after metamorphosis. Whatever crossed from caterpillar to moth therefore depended, at least partly, on when the learning had occurred.[2]

Taken together, these studies resist two simple pictures. Metamorphosis is not complete erasure: cells, structures and even some effects of previous experience can survive it. But neither is it straightforward continuity. A neuron may survive while abandoning the circuit that once gave it its role. Old relationships disappear, new ones form, and surviving elements may acquire functions they did not previously possess.

The organism remains continuous with what came before. Yet continuity does not require the preservation of the old architecture.

That is where the biological fact begins to become philosophically interesting.

Perhaps profound transformation is sometimes like this as well. What survives may not survive by remaining what it was.

What We Imagine Transformation to Be

When we speak about spiritual transformation, we usually carry some picture of what transformation is supposed to look like. Often that picture remains implicit. We inherit it from religion, psychology, biographies of saints, modern ideas of self-development, or simply from the ordinary meaning of becoming “better.”

One common image is transformation as addition. The person remains fundamentally the same, but acquires something new: greater wisdom, more compassion, unusual experiences, better habits, perhaps a deeper understanding of reality. The old life continues, only enriched.

There is truth in this. We do learn. Capacities develop. What was previously impossible may become natural. But sometimes transformation does not feel like addition at all.

Another familiar image is the death of the old self. The previous person disappears and a new one is born. Religious conversion often uses this language, as do many accounts of awakening. It captures rupture very well: there are experiences after which returning completely to one's former way of seeing becomes impossible.

Yet psychologically, almost nothing happens so cleanly. Memories remain. Temperament remains. Old wounds remain. The body remains. Relationships may remain. Conditioning often survives long after a person's explicit worldview has changed. The old organism is rarely replaced wholesale.

A third image is purification. Something authentic has supposedly always been present beneath accumulated conditioning. Spiritual practice gradually removes fear, ego, attachment and false identification until the underlying nature becomes visible.

This too can describe something real. Much inner work does involve relinquishment rather than acquisition. But purification can easily suggest that transformation merely uncovers a finished person who was secretly there all along. It leaves less room for something equally important: genuine reorganization. Human beings do not only remove old patterns. They develop new capacities, new relationships and new ways of inhabiting the same world.

There is also a quieter assumption that may be even more widespread: after transformation, the basic architecture of one's life remains intact.

One remains a child to one's parents, a spouse, an employee, a member of a community, perhaps a practitioner within the same tradition. The hope is that these relationships will continue essentially as before, only now inhabited with greater consciousness.

Sometimes they do. But sometimes the people remain while the relationship changes. A parent may still be loved while ceasing to function as an inner authority. Work may continue while losing its power to determine personal worth. A spiritual tradition may remain precious while no longer supplying an identity that has to be defended.

Nothing obvious has disappeared, and yet the circuit is no longer the same.

Perhaps this is where the metaphor of metamorphosis becomes more exact than the familiar language of improvement, purification or rebirth. A neuron can survive while losing the connections through which it once performed its function.

Perhaps a person can as well.

What Metamorphosis Feels Like

Deep transformation is often described as though it were a moment of insight after which everything falls into place. Sometimes there are moments like that, but they are rarely the whole process. More often, something changes inwardly long before the surrounding life has had any chance to reorganize itself. The same people remain around us, the same responsibilities continue, the same house still stands, the same body wakes up in the morning, and yet the relations through which all of this once made sense have begun to shift.

A parent may still be loved deeply, yet no longer occupy the position of inner authority that once seemed natural. A partner may remain important while ceasing to carry the burden of providing identity, safety, or emotional regulation. Work may still matter enormously, but its power to determine self-worth may weaken. Even a spiritual path may remain precious while losing its function as a protected identity through which the rest of life is judged.

Nothing here necessarily looks dramatic from the outside. The same relationships may continue for years. The same names are used. The same rituals of everyday life remain. Yet internally, the old arrangement becomes increasingly difficult to inhabit.

This can be painful because relationships are built not only from affection, but also from expectations, habits and roles accumulated over time. Other people may continue speaking to an earlier version of us because that is the version through which they learned how to love us, rely on us, advise us or feel needed by us. We may also continue responding through old reflexes after we have outgrown them. A familiar tone of voice can still awaken obedience. A disappointed look can still evoke guilt. A request can still carry the emotional weight of a command long after we have understood intellectually that we are free to refuse it.

For a while, the old and new arrangements coexist. A person may know that they no longer need a parent's approval and still feel distressed by parental disappointment. They may know that a relationship has become unhealthy and still experience separation as a wound. They may understand that work should not define them and still feel devastated when professional recognition disappears. Intellectual understanding does not immediately undo patterns learned over years.

This is one reason transformation can feel much less luminous than its later descriptions suggest. Retrospectively, people speak of awakening, release, independence, recognition. While it is happening, the experience may be closer to confusion, irritation, grief, loneliness, and the repeated need to make ordinary decisions differently from how one made them before.

There is often no single heroic moment. Instead there are situations in which an older pattern quietly asks to be repeated. Someone expects an explanation, and we discover that we no longer want to give one. Someone becomes disappointed because we have said no, and their disappointment no longer automatically becomes our responsibility. A relationship asks us to return to a familiar dependence because that dependence once made everyone feel secure, and we find that returning now would require denying something that has already changed inside us.

This can be especially difficult when love remains. If a relationship were entirely hateful, separation would be simpler. The deeper transformations often occur where affection and limitation are mixed together. We may continue loving a parent while recognizing that their anxiety has been woven into our own decisions for years. We may remain grateful to a workplace, a tradition or a community that shaped us while also seeing that its authority over us has ended.

Then the task is no longer merely to leave or remain. It is to learn how to relate differently.

Sometimes the relationship survives this change. Sometimes it becomes gentler after a period of conflict. Sometimes distance becomes necessary. People who once occupied the center of our emotional world may move outward without disappearing from it. Something that looked indispensable may reveal itself to have been only one particular form through which closeness was expressed.

This is where the image of metamorphosis becomes especially precise. The surviving neuron is still recognizably the same cell, carrying its own history through the transformation. Yet the network around it has changed so profoundly that its former function can no longer simply continue. It may connect elsewhere. It may participate in another system. Its significance changes because its relationships have changed.

Human transformation can feel similar. Much of the old life survives: memory, affection, temperament, responsibilities, the body's traces of what came before. What changes is the architecture of dependence and meaning.

A parent can become a person rather than an authority. Work can become a craft rather than a verdict on one's worth. Spiritual practice can become something lived rather than something used to maintain an identity.

And these changes do not always arrive through deliberate spiritual practice. Life itself can force them. Illness can alter the relationship to the body more deeply than years of contemplation. Betrayal can expose forms of dependence that affection had concealed. Loss can reveal how much of one's sense of safety had been outsourced to circumstances. Parenthood can reorganize priorities more radically than abstract philosophy. Long periods of pressure can make old assumptions impossible to maintain simply because reality keeps contradicting them.

There does not need to be any hidden benevolent design behind this. Human beings often suffer because bodies fail, relationships break, institutions become cruel, families remain trapped in old patterns, and history becomes violent. The causes can be entirely ordinary and sometimes senseless.

Yet once a structure has been shaken, something still has to happen with what has been revealed.

A person may emerge from such periods with fewer illusions about what can be guaranteed, while also becoming more capable of relating without possession or dependence. They may discover that gratitude does not require obedience, that closeness does not require fusion, and that belonging does not have to mean surrendering one's own center.

These shifts are rarely impressive from the outside. They may appear in very small acts: saying no without hatred, accepting another person's disappointment without panic, continuing to care without returning to an old role, allowing someone we love to misunderstand us without immediately abandoning ourselves in order to correct their image.

Over time, the old circuitry stops feeling inevitable. The world may still look almost unchanged. The same people may sit at the same table, the same work may wait in the morning, the same responsibilities may remain. Yet things that once stood at the center move outward. Some relationships lose their power to define us and become freer precisely because they no longer need to carry that burden.

Perhaps this is what spiritual metamorphosis often feels like from inside: not becoming another creature overnight, but gradually discovering that the life which once organized us can remain present without continuing to govern us in the same way.

The World Does Not Have to Disappear

Long before neuroscience gave us the strange image of neurons surviving while their circuits are rebuilt, Utpaladeva described spiritual transformation in a way that seems surprisingly close to it.

In the Śivastotrāvalī, he does not usually imagine liberation as the disappearance of ordinary experience. The world remains extraordinarily present: pleasure and pain, friends and relatives, perception, longing, devotion. What changes is the relation through which all of this is lived.

One verse says:

sarva eva bhavallābhahetur bhaktimatāṃ vibho |
saṃvinmārgo ’yam āhlādaduḥkhamohais tridhā sthitaḥ || 1.10 ||

“O Lord, for those endowed with devotion, this entire path of consciousness—appearing threefold as joy, suffering and delusion—becomes a means of reaching You.”

The verse is striking because Utpaladeva does not divide experience into the spiritual and the unspiritual. Joy, suffering, even moha—confusion, bewilderment, the contracted condition in which things are not seen clearly—remain within the same saṃvinmārga, the pathway of consciousness.

Kṣemarāja's commentary makes the point wonderfully concrete. The path in question is the ordinary movement of cognition through which we know things such as blue and yellow. It is not another world concealed behind this one. For the devotee, this very pathway becomes the means by which the supreme knower is approached.

The experiential material remains. Its function has changed.

Something that once participated only in contraction can become part of recognition. The same joy, the same pain, the same stream of ordinary perception now belongs to another circuit.

Utpaladeva makes the movement still more radical elsewhere:

jagad idam athavā suhṛdo bandhujano vā na bhavati mama kim api |
tvaṃ punar etat sarvaṃ yadā tadā ko ’paro me ’stu || 11.1 ||

“This world, or friends, or relatives—none of these is anything of mine. But when You are all this, what could then remain other to me?”

At first the verse almost sounds like renunciation. The world is not mine; friends and relatives are not mine; nothing is mine.

But Utpaladeva does not stop there. The second half reverses the movement completely: You are all this.

The relationships have not been annihilated. Friends remain friends. Relatives remain relatives. The world has not dissolved into an empty abstraction. What has disappeared is one particular way of possessing and being possessed by them. The movement is not simply from attachment to indifference. It is from “mine” to something wider.

This may be one of the subtler forms of spiritual metamorphosis. What we love does not have to disappear for the structure of dependence around it to change. The body does not have to be despised because it cannot provide permanent security. The world does not have to become meaningless because it no longer defines who we are.

The same people may still sit around the same table. The same responsibilities may wait in the morning. Joy and pain will return.

And yet the relations by which these things once organized the self can be profoundly altered.

This is why metamorphosis may be a better image than escape. Much of a human life may survive spiritual transformation, just as the larval neuron may survive the destruction of its old circuit. But what survives no longer has to mean what it once meant.

The world does not have to disappear.

Perhaps it is enough that it no longer occupies the same place within us.

What Remains

The metaphor has limits.

An insect nervous system is not a human life, and neural remodeling does not prove anything about liberation, reincarnation, or a metaphysical Self. Biology can show us continuity through radical reorganization; it cannot tell us what spiritual realization ultimately is.

But metaphors do not need to prove in order to illuminate.

What this one offers is a different image of transformation. Perhaps we do not always become free by abandoning the world that formed us. Often much of it remains: the same body, the same family, the same memories, the same work, the same unfinished history.

What changes is the circuitry of dependence. Things that once defined us become things we can simply relate to. This change is rarely clean. Old connections continue firing long after they have ceased to fit. Other people may still address an earlier version of us, and we may repeatedly return to familiar patterns simply because they are familiar.

Metamorphosis is therefore not necessarily a moment. It can be a long interval in which the old architecture has already become impossible, while the new one is still learning how to live. This may be why genuine transformation can feel less like illumination than like uncertainty, grief, resistance and rearrangement.

Slowly, another possibility appears.

We may discover that we can love without returning to the old dependence. We can remain grateful without surrendering our boundaries. We can carry memories without allowing them to dictate the future. We can remain close to people who formed us while no longer asking them to tell us who we are.

Nothing about this requires contempt for the earlier life. The old structures may have protected us, nourished us, and carried us for years. Some may still deserve tenderness. They simply no longer need to carry the weight of our identity.

And perhaps that is one of the quieter signs that metamorphosis has actually occurred: not that the past has been defeated, but that it can finally be held without being obeyed.

The same people may remain. The same memories may return. The same world may still contain uncertainty, loss, beauty and pain.

But something in the relationship has softened and become freer.

We no longer need everything we love to save us.

And we no longer need to destroy it in order to become ourselves.

The world may remain almost exactly where it was.

But we can meet it now from a place that is more our own.

Notes

[1] James W. Truman, Jacquelyn Price, Rosa L. Miyares & Tzumin Lee, “Metamorphosis of memory circuits in Drosophila reveals a strategy for evolving a larval brain,” eLife 12 (2023), e80594. doi: 10.7554/eLife.80594 (https://elifesciences.org/art[icles/80594)

[2] Douglas J. Blackiston, Elena Silva Casey & Martha R. Weiss, “Retention of Memory through Metamorphosis: Can a Moth Remember What It Learned As a Caterpillar?”, PLOS ONE 3.3 (2008), e1736. doi: 10.1371/journal.pone.0001736 (https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0001736)