🚫 That assumption is wrong. Or rather, it is far too simple, and the oversimplification has shaped the design of every therapeutic stimulation device currently in clinical use.

🔎 Here’s what we found. When you deliver electrical pulses to the brain through a microelectrode, you don’t just activate nearby neurons. At certain frequencies and temporal patterns, you inhibit neural network activity. Not individual neurons, the biophysics of direct cathodic stimulation make it nearly impossible to inhibit a single cell with an extracellular electrode. But networks? Networks can absolutely be inhibited, through a mechanism that exploits something the field had been overlooking: inhibitory neurons.

🛑 Inhibitory interneurons, particularly the parvalbumin-expressing fast-spiking type, can sustain firing rates above 100 Hz. Excitatory neurons typically cannot reliably fire above 15-20 Hz. When you deliver high-frequency stimulation, you preferentially drive inhibitory networks. If you then pause at the right moment, while excitatory neurons are in their absolute refractory period, the inhibitory drive suppresses excitatory activity during the pause. The result is a net reduction in network output, inhibition, achieved through stimulation.

We demonstrated this using in vivo two-photon calcium imaging, watching the activity of individual labeled neurons in living mouse cortex during and after stimulation. The finding overturned dogma that had stood unchallenged since the early 20th century.

The finding has direct clinical relevance. Depression, epilepsy, schizophrenia, and chronic pain all involve excitation-inhibition imbalances. If stimulation can be used not just to activate but to selectively suppress overactive circuits, the therapeutic possibilities expand considerably.

It also explains something BCI users know experientially but researchers struggled to account for: that the sensation evoked by electrical stimulation fades. The inhibitory recruitment we identified is one mechanism underlying that fading, and understanding it is the first step toward designing stimulation patterns that sustain perception rather than letting it decay.

More to come.

Review: https://lnkd.in/enHUqypN
Inhibitory: https://lnkd.in/ecFihBRm
Temporal Pattern:https://lnkd.in/dXkpMmQ
Freq: https://lnkd.in/e2d39Dvc
Waveform: https://lnkd.in/e-2b4Jq5
Biomimitic: https://lnkd.in/gm2x_AgM

#Neuroscience #Neuromodulation #BrainStimulation #Neurotechnology #BrainComputerInterface

⚠️ The BCI field has operated for decades as though it were. The standard way to evaluate tissue health near an implanted electrode is to count cells and measure impedance. Neurons present, spikes detectable, device biocompatible. That framework misses something fundamental.

🧱 Neurons don’t encode information alone. They encode it through coordinated activity with their neighbors, through precise timing relationships in local circuits. A neuron that fires but has lost its functional coupling to the surrounding network is, from a decoder’s perspective, noise.

💑 We tested this directly. Using chronically implanted arrays in mouse cortex, we tracked whether pairs of neurons maintained correlated firing patterns over weeks. Functional connectivity, how reliably one neuron’s activity predicts another’s, degraded substantially near the electrode, even among neurons that remained individually detectable. They were alive. Spiking. But uncoupled from their neighbors. The local circuit was fragmented.

📉 The degradation was layer-dependent. Different cortical layers showed different vulnerability profiles, meaning the failure is structured, not random. Any intervention treating all cortical tissue as equivalent will miss the mark.

🎞 This reframes what “biocompatibility” should mean for neural interfaces. The traditional definition (does the tissue survive?) is necessary but insufficient. What matters is functional biocompatibility: does the tissue still compute? (FDA definition of biocompatibility is functional)

📊 Our data say that for tissue closest to the electrode, the answer is progressively no, and this functional degradation occurs before the structural markers the field relies on would raise concern. By the time histology looks bad, the network has been impaired for weeks.

🗓 Connect this to earlier posts. Oligodendrocyte injury, vascular disruption, lysosomal dysfunction, each can independently degrade functional connectivity without killing the neuron. Together they create a microenvironment where neurons survive as individuals but fail as a network.

🎥 Recording quality cannot be evaluated by spike count alone. We need metrics that capture whether recorded populations retain their network structure. A channel that detects a neuron is not the same as a channel that detects a neuron doing something meaningful.

Longitudinal Functional connectivity: https://lnkd.in/ePjwGw2S
Alive but Silenced: https://lnkd.in/e6bgMBAt
Review: https://lnkd.in/eYi75Sxi

#Neuroscience #Neurotechnology #BrainComputerInterface #NeuralEngineering #Bioengineering #FunctionalPerformance

The brain is the most metabolically demanding organ in the body. It consumes roughly 20% of the body’s energy despite representing only 2% of its mass. That energy is delivered through a dense network of blood vessels, regulated in real time by a system called neurovascular coupling, the mechanism by which active brain regions signal their need for more blood flow and receive it within seconds.

🚧 When an electrode is implanted, this system is disrupted. Vessels are severed or compressed during insertion. Pericytes, the cells that regulate capillary diameter and blood flow, constrict in response to injury. The result is a local reduction in tissue oxygenation around the electrode in the days and weeks following implantation.

🔇 We showed that this deoxygenation has direct consequences for neural activity. Neurons adjacent to the implant are silenced, not because they are dead or damaged in the conventional sense, but because they lack the metabolic resources to sustain activity. When we provided strong direct electrical stimulation, those neurons responded. They were alive. They were just quiet, rationing energy the way any system does when its supply is constrained.

😶 This has a deeply uncomfortable implication for how we interpret BCI recordings. When a researcher or clinician observes decreased neural activity around a chronically implanted electrode, the standard interpretation is neuronal loss. Our data suggest that at least some of what looks like neuronal loss is actually neuronal silence driven by metabolic stress. The neurons are there. They’ve just gone dark.

🩺 The distinction matters enormously for intervention strategy. If neurons are dead, you need to prevent death. If neurons are metabolically suppressed, you potentially need to restore the energy supply, a very different problem with a very different solution.

🔬 This is why my lab has become increasingly focused on oligodendrocytes, pericytes, and the neurovascular system as targets, not just the electrode-tissue interface itself.

Metabolic Stress & Silencing: https://lnkd.in/e6bgMBAt
Review: https://lnkd.in/e7MrVCc7
Pericytes: https://lnkd.in/edzheqNu
Oligo: https://lnkd.in/ePXYRr2C
Metabolic Stress& Silencing2: https://lnkd.in/eZ_7ZsTN
Metabolic Stress3: https://lnkd.in/e8FdNNFw
Review 2: https://lnkd.in/e_giHFkU

#Neuroscience #BrainHealth #Metabolism #BrainComputerInterface #Bioengineering

⏳ That framing was wrong, and it cost the field decades.

My lab has spent years studying the non-neuronal cells of the brain, oligodendrocytes, astrocytes, microglia, pericytes, and what we’ve found repeatedly is that these cells are not passive bystanders to what’s happening at the electrode interface. They are active participants in determining whether the device continues to work.

🔎 Oligodendrocytes are perhaps the most striking example. These cells wrap axons in myelin, the insulating sheath that most people know as the thing that speeds up nerve conduction. The standard story is that myelin is about speed. That’s true, but it’s incomplete.

🔬 We discovered something more fundamental. Oligodendrocytes dramatically reduce the metabolic cost of neural activity. Every time a neuron fires an action potential, sodium and potassium ions cross the membrane and have to be pumped back. That pumping requires ATP. Myelin restricts where that ion exchange happens, dramatically reducing the total energy bill for sustained neural firing.

😫 When oligodendrocytes are depleted near an implanted electrode, neurons don’t slow down. They fatigue. They can’t maintain elevated firing rates under sustained input for more than a fraction of a second. The device is recording from neurons that have, in metabolic terms, run out of fuel.

🧩 This finding reframed an observation that had puzzled BCI researchers for years: why do recordings degrade even when the electrode looks fine and neurons are still alive nearby? Part of the answer is oligodendrocytes. The neurons are there. They’re just exhausted.

Oligo Review: https://lnkd.in/edpJ2zzy
Oligodendrocyte Precursor Cells: https://lnkd.in/eyz34b4
Oligodendrocytes: https://lnkd.in/ePXYRr2C
Oligo Failures/Fatigue: https://lnkd.in/egAwPGv

#Neuroscience #Neurotechnology #Glia #BrainHealth #NeuralEngineering #BCI #Neurotech

📈 BCIs are having a moment. Billions in private capital. Headlines about paralyzed patients moving cursors & typing text. Real progress, built by talented engineers solving hard problems.

🦯 But here’s what most people don’t see.

🛫 Every one of those achievements depends on basic science discoveries made 20~30 yrs ago. Publicly funded research that characterized how neurons fire, how electrodes interact with tissue, how the brain reorganizes after injury. That knowledge is the runway. The devices are the aircraft.

🚧 Right now, we are building faster planes on a runway that nobody is extending.

🔬 I’ve spent 20 years studying what happens at the boundary between implanted devices & living brain tissue. The biology is humbling. Glial cells encapsulate electrodes. Blood vessels rupture and never fully recover. Neurons die or get displaced. The immune system mounts a chronic response that degrades signals over months~years.

🧬 These are not engineering problems. You cannot solve them with better materials or more channels or faster decoding algorithms. They are biological problems, & they require basic science to understand.

💳 Venture capital will not fund this work. There is no quarterly earnings case for astrocyte biology. No Series B for characterizing neurovascular disruption at the electrode interface. That is not a criticism of VC. It is a description of what VC is designed to do, which is build products, not generate foundational knowledge.

🏥 NIH is the only institution with both the mandate and the scale to fund this kind of research. And right now, OMB is freezing NIH funding. Paylines are compressed. Review panels increasingly penalize DISCOVERY-oriented proposals that cannot promise translational outcomes within 5 yrs. Funding delays disproportionately hit new grants.

🇨🇳 Meanwhile, other nations are investing heavily in exactly this space with explicit patience for long-term discovery. We should not assume that competitors lack the capacity for original scientific contribution. History has repeatedly punished that assumption.

🔎 Every unfunded basic science grant cycle means specific biological questions about chronic BCI failure go unanswered. Those unanswered questions become the ceiling on what the next generation of devices can achieve, regardless of how much private capital flows into engineering.

⏱️ Translation without basic science is a plane accelerating toward the end of a runway that gets shorter every year.

If we want BCIs that last a lifetime in the human brain, we need to fund the science that explains why they currently don’t.

https://www.bioniclab.org/links/basicscience

#neurotech #BCI #NIH #basicscience #discovery #WhyBCIsFail ##Innovation #Neurotechnology #BrainComputerInterface #NeuralEngineering #Bioengineering #FunctionalPerformance #Neuroscience

🗓️ Over the first few days following implantation, microglia migrate their cell bodies toward the injury site. Astrocytes, star-shaped support cells that normally maintain the chemical environment around neurons, swell and extend processes toward the device. NG2 cells, precursors to several cell types, begin dividing and moving in. Pericytes, the cells that regulate blood flow through capillaries, constrict nearby vessels. Within a week, the electrode is encapsulated in a dense cellular sheath.

⛔ This process, the foreign body response, is the brain doing exactly what it should do when faced with an injury it cannot remove. The problem is that the brain cannot distinguish between a harmful splinter and a therapeutic device. It treats them identically.

🦠 The cellular sheath that forms around a chronically implanted electrode does several things that are bad for recording. It increases the electrical impedance between the electrode and the neurons it’s trying to listen to. It pushes neurons physically away from the recording site. And it creates a chronically inflamed microenvironment that is toxic to the very cells the device is trying to monitor.

🤝 What surprised us most in studying this process wasn’t the glial response itself, that was well known. It was the timing. The different cell types respond on very different time scales: microglia within minutes, astrocytes within hours, NG2 cells within days. This orchestration matters because it means there are distinct windows during which intervention might redirect the response. A drug delivered on day one would encounter a very different biological environment than the same drug delivered on day seven.

🕰️ The field spent decades trying to make electrodes that the brain would ignore. We’ve had to accept a harder truth: the brain will not ignore a foreign object. The goal has to shift from avoiding the response to redirecting it.

Microglia: https://lnkd.in/e6Uc4YPw
Astrocytes: https://lnkd.in/e2wFzPCT
NG2: https://lnkd.in/eyz34b4
Oligodendrocytes: https://lnkd.in/ePXYRr2C
Pericytes: https://lnkd.in/edzheqNu
Neuron: https://lnkd.in/enJAmMwi
Neuronal Silencing: https://lnkd.in/e6bgMBAt
Review 1: https://lnkd.in/e7MrVCc7
Review 2: https://lnkd.in/ebB5H4K

#Neuroscience #BrainComputerInterface #Immunology #NeuralEngineering

🧠 Every time the brain moves, and it moves constantly (with every heartbeat, every breath, every shift in posture), a rigid electrode anchored to the skull shifts relative to the soft tissue around it. This micromotion is measured in microns, but at the cellular scale, microns matter. Cells at the electrode surface experience repeated mechanical strain. Blood vessels are tugged. The tissue never reaches equilibrium because the mechanical insult never stops.

🗺️ We mapped the design landscape for this problem in a systematic review of how material properties (stiffness, size, surface chemistry, geometry) interact with the biological response. The picture that emerged was sobering. No single material parameter predicts outcome. Stiffness interacts with cross-sectional area. Surface chemistry interacts with geometry. The design space is high-dimensional, and most of it is unexplored.

🔍 One approach our lab pioneered was moving to carbon fiber microelectrodes. These are roughly 7 microns in diameter, thin enough that the tissue can move around them rather than being displaced by them. We showed in Nature Materials that these ultrasmall probes could record single-unit neural activity with dramatically less tissue displacement during insertion and reduced chronic inflammation compared to conventional silicon devices.

📑 But here is the harder lesson. Making electrodes smaller and more flexible helps. It does not solve all the problem. Even our carbon fiber probes, among the smallest functional recording electrodes ever implanted, still trigger a biological response. The foreign body reaction described in the next post occurs around flexible devices too, just at reduced magnitude. The brain does not distinguish between a large insult and a small one in kind, only in degree.

⏳ This is why materials science alone cannot fix BCI longevity. Better materials buy time. They reduce the severity of the initial injury and the magnitude of the chronic response. But they do not eliminate the biological cascade that ultimately determines whether the device keeps working. Understanding that cascade requires looking past the electrode and into the cells surrounding it.

Ultrasmall Electrodes: https://lnkd.in/epWswUdi
Mechanical: https://lnkd.in/etnqjYRA
Size and Neuron: https://lnkd.in/ei2W5HyW
Review 1: https://lnkd.in/e7MrVCc7
Review 2: https://lnkd.in/eW3rAXGB

#Neuroscience #Neurotechnology #BrainComputerInterface #MaterialsScience #Bioengineering #micro #nano

🦠 The moment an electrode enters brain tissue, something remarkable happens. Microglia, the brain’s resident immune cells, extend their processes toward the insertion site within seconds to minutes. Not hours. Seconds. We watched this happen in real time using two-photon microscopy, imaging living mouse brain through a small window in the skull as the electrode descended. The microglia moved like fingers reaching toward a splinter.

⌛ This immediate response sets the stage for everything that follows. The brain doesn’t wait to see whether the device is harmful. It treats any foreign object as a threat and begins responding before any damage has even been assessed.

🚧 At the same time, nearby blood vessels, some severed during insertion, others simply compressed as tissue deforms, begin to leak. The blood-brain barrier, the brain’s carefully maintained boundary between circulation and neural tissue, is disrupted. Proteins that normally stay in the bloodstream spill into brain tissue, and this triggers a cascade of inflammatory signals.

⚠️ Here’s what this means practically: two electrodes implanted by the same surgeon, in the same brain region, with the same device, on the same day, can perform very differently. Not because of anything that happened after implantation, but because of what happened during the ten seconds it took to insert them. Which blood vessels were nicked. How much the tissue compressed. Whether the trajectory grazed an arteriole or threaded between capillaries.

🔦 We were the first to show that this insertion variability has lasting consequences for how the device performs months later. That finding helped inform image-guided surgical approaches now used in next-generation BCI systems.

📣 The engineering implication is uncomfortable: even a perfect device, perfectly fabricated, can be compromised in the operating room before it ever records a single spike.

Blood Vessels: https://lnkd.in/ekVrUTmp
Microglia: https://lnkd.in/efv-dkfr
Astrocytes: https://lnkd.in/e2wFzPCT
Oligodendrocyte Precursor Cells: https://lnkd.in/eyz34b4
Engineering: https://lnkd.in/epWswUdi

#Neuroscience #Bioengineering #BrainComputerInterface #Immunology #NeuralEngineering