Denis Katz, MD, MHA
Founder, Salience Clinical

Reframing Depression: Beyond Chemistry

For much of modern psychiatry, major depressive disorder (MDD) has been understood through the lens of neurochemistry—an imbalance in serotonin, norepinephrine, or dopamine signaling. This paradigm has driven decades of therapeutic innovation.

But its limitations are now clear.

A significant proportion of patients remain treatment resistant. Among those who respond, relapse is frequent. Incremental gains from traditional pharmacology are becoming harder to achieve, suggesting that synaptic modulation alone may no longer be sufficient to meaningfully shift long-term outcomes.

The field is approaching an inflection point.

The next evolution in neuropsychiatry will not come from refining chemistry alone.
It will emerge from understanding and intervening in the brain’s architecture.

What Architecture Really Means

In this context, architecture refers to the organization and interaction of large-scale brain networks: how they connect, compete, and dynamically switch to govern cognition and behavior.

Advances in functional neuroimaging and computational neuroscience have converged on a consistent finding: depression is not localized dysfunction it is distributed network imbalance.

At the center of this model is the triple network framework:

• Salience Network (SN): Directs attention by identifying what matters, and orchestrates transitions between brain states
• Central Executive / Frontoparietal Network (CEN/FPN): Supports cognitive control, planning, and goal-directed action
• Default Mode Network (DMN): Enables introspection and self-referential processing, but when dysregulated, reinforces rumination

What defines healthy function is not the strength of any single network, but the balance and timing of their interactions.

Depression as a Network Disorder

In MDD, this balance breaks down.

Research consistently shows:

• Reduced opposition between DMN and executive networks
• Aberrant coupling between salience and both DMN and CEN systems
• Impaired ability of the salience network to shift the brain between internal and external modes

The result is a system that becomes stuck overweighted toward self-referential processing, with insufficient recruitment of cognitive control.

In treatment-resistant depression, these disruptions are often more severe, reflecting deeper instability in network coordination.

This reframes depression fundamentally:

It is not simply a disorder of neurotransmitters.
It is a disorder of network dynamics and control systems.

The Strategic Blind Spot in Current Treatments

Most existing therapies were not designed with this architecture in mind.

• Pharmacologic treatments primarily adjust synaptic signaling
• Neuromodulation approaches (rTMS, ECT, DBS) alter activity in localized regions

These interventions can be effective but they are not explicitly designed to restore network balance, proportionality, or switching efficiency.

In other words:

• We modulate signals
• But we rarely recalibrate systems

This gap helps explain a critical clinical reality: symptom improvement without durable remission.

If network-level dysfunction persists, relapse risk remains.

A New Question for CNS Innovation

This shift in understanding leads to a more precise challenge:

Can we design therapies that restore how brain networks interact not just how neurons fire?

Answering this question requires moving from a molecular model of disease to a systems-level intervention strategy.

Toward Network-Centric Therapeutics

The emerging blueprint for precision psychiatry is inherently architectural:

• Connectivity-driven stratification: Defining patient subtypes based on network patterns rather than symptom clusters
• Network-based endpoints: Measuring connectivity, flexibility, and switching dynamics alongside clinical outcomes
• Closed-loop neuromodulation: Adapting stimulation in real time based on brain-state biomarkers
• Plasticity-enhancing agents: Therapies that reshape network organization, not just synaptic transmission
• Digital and behavioral interventions: Designed to actively engage executive systems and disrupt maladaptive network dominance

This is not a rejection of neurochemistry it is its integration into a broader systems framework.

Implications for Drug Development and Trial Design

1. Rethinking Efficacy

Efficacy must extend beyond symptom scales to include:

• Restoration of network balance
• Improved switching dynamics
• Increased system flexibility

These measures can provide earlier and more mechanistic insight into treatment response.

2. Reducing Heterogeneity

Network biomarkers offer a path to:

• Stratify biologically coherent patient populations
• Reduce signal dilution
• Improve trial efficiency and success rates

3. Redefining Endpoints

Static clinical snapshots are insufficient.
Dynamic measures of network behavior may serve as leading indicators of durable response.

4. Evolving the Narrative

The “chemical imbalance” model no longer reflects the state of the science. A network-based framework:

• Aligns with current evidence
• Supports integrated drug-device strategies
• Enhances credibility with regulators and payers

From Concept to Practice

Consider a future treatment-resistant depression program:

• A rapid-acting neuroplasticity agent primes network reorganization
• Connectivity-guided rTMS targets specific circuit imbalances
• Outcomes are measured not only by symptom change, but by normalization of network interactions

This is what it means to operationalize architecture.

The Competitive Divide

The field is entering a new phase:

• Network neuroscience is now actionable
• Computational tools can extract predictive signatures from complex brain data
• Neuromodulation technologies are increasingly programmable and adaptive
• Multimodal datasets enable biologically grounded stratification

The implication is strategic.

Organizations that integrate network architecture into development will define the next generation of CNS therapeutics.

Those that remain focused solely on chemistry will encounter diminishing returns.

The Salience Clinical Perspective

At Salience Clinical, we translate systems neuroscience into development strategy.

Our focus is practical:

• Embedding network biomarkers into trial design
• Aligning mechanism with measurable outcomes
• Integrating clinical, regulatory, and commercial strategy

We do not treat architecture as theory.
We treat it as a design principle.