Design, implement and verify in vitro the control firmware of a neurostimulator that elicits localized neuronal responses for a thalamic visual prosthesis.
Posted on by Pablo Sarabia Ortiz
Design, implement and verify in vitro the control firmware of a neurostimulator that elicits localized neuronal responses for a thalamic visual prosthesis

Introduction

Achieving precise and localized neuronal stimulation is one of the main challenges in neurotechnology. Current approaches often suffer from low spatial specificity, which can lead to unintended activation of surrounding tissue and reduced therapeutic efficiency. A method capable of eliciting spatially localized responses would represent a significant advancement, allowing more targeted interventions, minimizing side effects, and enabling the development of high-resolution neuroprosthetic systems.

Keywords

Brain-Computer Interface (BCI), Visual prosthesis, Lateral geniculate nucleus (LGN),
Neurostimulator, Beamforming, Temporal Interference Stimulation (TIS), Deep brain stimulation
(DBS), Firmware, Neurotechnology, In vitro.

Objective

The objective of this master’s thesis is to design, implement, and verify in vitro the control firmware for a neurostimulator capable of producing localized neuronal responses. This work is framed within the VISNE project, which seeks to advance thalamic visual prostheses. The strategy explored combines two advanced stimulation techniques: beamforming and temporal interference stimulation (TIS), both aimed at improving spatial precision and overcoming the low specificity of conventional neurostimulation.

Electrode Setup for In Vitro Measurement

Testing Electrode Setup

Solution

Experimental Setup for electrode stimulation tests
The experimental setup for in vitro verification

To achieve this, a programmable four-channel neurostimulator was used. The device can generate multiple synchronized waveforms, including biphasic and sinusoidal signals, enabling the shaping of the electric field inside neural tissue. First, computational simulations of beamforming and TIS were performed to predict how stimulation patterns could be steered toward specific regions. Then, in vitro experiments were conducted using the neurostimulator and a custom experimental setup to validate these methods.

Results

The results showed strong spatial correlations between simulations and experimental measurements, confirming that both beamforming and TIS can focus electrical stimulation effectively. However, challenges were found in reproducing field amplitudes with high accuracy, as statistical analyses (MAE, RMSE) revealed residual errors in the measurements. Among the two techniques, TIS proved particularly promising, successfully generating low-frequency interference envelopes with strong spatial selectivity.

Temporal Interference results comparison with simulation

Design and Implementation of a Device for Capturing Biological Signals Applied to the Treatment of Ischemic Stroke.
Posted on by rookie
Ikki PCB design

Introduction

This work is part of the STRIKE project, a multidisciplinary initiative aimed at developing new therapeutic strategies for the treatment of ischemic stroke, one of the leading causes of death and disability in Spain and worldwide. STRIKE integrates three techniques: transcranial magnetic stimulation (TMS), implantation of mesenchymal stem cells encapsulated in silk fibroin, and electrical stimulation of the auricular branch of the vagus nerve (aVNS).

In this context, the Ikki device has been designed and implemented a portable system for acquiring biological signals, specifically electrocardiogram (ECG) in rodents and electroencephalogram (EEG) in humans. This work primarily focuses on the electrical stimulation of the auricular branch of the vagus nerve, although it is partially related to transcranial magnetic stimulation. The main goal is to enable real-time monitoring of physiological responses to the applied therapies, thereby facilitating personalized treatment and experimental validation of the proposed techniques. The device has been validated in a real-world setting through human trials.

Keywords

Electrocardiogram, electroencephalogram, biological signals, electrophysiology, biomedical
device, portable, low power consumption, vagus nerve, ischemic stroke, treatment, embedded
system.

The problem

Clinical Context

Ischemic stroke accounts for more than 80% of stroke cases. Conventional treatment is based on early reperfusion and physical rehabilitation, but neurological recovery remains limited. Therefore, new strategies are needed to complement current treatments and improve neuroprotection and brain regeneration. The STRIKE project was born from the development of these new strategies.

Technological Need

To experimentally validate the techniques proposed in the STRIKE project, it is essential to have a device capable of accurately acquiring physiological signals in a portable, non-invasive, and user-friendly manner for researchers. ECG and EEG signals allow for the evaluation of the impact of therapies on the nervous and cardiovascular systems and are fundamental for establishing a personalized treatment approach.

CTB ADC and stimulator

Acquisition system for ECG and stimulation used in the CTB.

Currently, experiments conducted at the Center for Biomedical Technology (CTB) use very large devices that hinder researchers due to their size. Therefore, the long-term goal is to develop a device with a “closed-loop approach.” To achieve this, the signal acquisition device is developed first, and later stimulation will be integrated into the same device.

Proposed Solution

The Ikki device has been developed as a comprehensive solution for acquiring and transmitting biological signals in the context of ischemic stroke treatment. Its design meets criteria of portability, low energy consumption, data capture precision, and ease of use in experimental and clinical environments. The system has been divided into hardware and software components.

Hardware Development (HW)

Ikki PCB design
Ikki V1.3

The complete hardware system has been built around a custom board integrating the following modules:

  • MSP430FG479 Microcontroller: Responsible for acquiring signals from the acquisition circuits. It includes built-in SD16-type ADCs. This is the main microcontroller of the entire system.
  • Signal Acquisition Circuits: Composed of several modules that allow analog processing of the signals to be captured, with filtering and amplification adapted to each signal type.
  • Power Supply System: Composed of a PMIC, a linear regulator, and an inverter that enable symmetrical power supply to the entire system.
  • Communications: Includes test points that allow data collection through the main microcontroller.
  • Connectors and Electrodes: Adapted for use in humans and rodents, ensuring secure and stable connections during acquisition.

The design has gone through several iterations, from initial prototypes to the final version Ikki V1.3, optimized for real-world testing. The quality of the acquired signals has been validated through comparisons with commercial systems.

Software Development(SW)

The software is divided into four layers:

  1. Acquisition Layer:
    • Developed in C using Code Composer Studio.
    • Programs the main microcontroller MSP430FG479.
    • Acquires data via the microcontroller’s built-in ADCs, processed through the acquisition circuits.
    • These data are then sent in a predefined format via SPI or UART to the bridge layer.
  2. Communication layer:
    • Defines a state machine to differentiate data acquired from various channels by the main microcontroller.
  3. Bridge layer:
    • Programs an ESP32 using ArduinoIDE.
    • Receives data from the acquisition layer via SPI/UART and forwards them via BLE.
    • Enables wireless functionality of the device.
  4. Visualization layer:
    • Programmed in Python.
    • Establishes a connection with the bridge layer and displays the data received via BLE on a device screen, such as a laptop.

Mesa redonda – Modificación de conductas como apoyo a las operaciones
Posted on by Octavio Nieto-Taladriz

Academia de las Ciencias y las Artes Militares – Sección de Prospectiva Tecnológica

El pasado 7 de mayo tuvo lugar una mesa redonda en la Academia de las Ciencias y las Artes Militares (ACAMI) organizada por nuestro compañero Octavio Nieto-Taladriz, de la que es Académico. Además de tener un formato presencial, la mesa redonda se retransmitió y el vídeo puede verse en el siguiente link.

Resumen

En la actualidad las operaciones multidominio están teniendo un fuerte auge, un gran impacto en las nuevas operaciones y hay una gran preocupación sobre cómo abordarlas, tanto bajo el punto de vista ofensivo como defensivo. Por otra parte, la sección de Prospectiva Tecnológica de la ACAMI pretende con esta mesa redonda sembrar la semilla de cual podría ser un aspecto futuro de especial relevancia como es el poder modelar el comportamiento humano y con ese conocimiento ser capaces de crear estrategias tanto de ataque como de defensa.

Con la amplia extensión de las redes sociales y su capacidad de influencias en los individuos se abre un nuevo mundo de modificación de conductas, como todos podemos ver está ocurriendo en los últimos años. Por otra parte, la existencia de herramientas de procesado de datos a gran escala y la realización de operaciones de inteligencia y control sobre ellos pueden permitir la elaboración de estrategias complejas de modificación de conductas individuales dentro de un colectivo. Un paso relevante es el paso desde la influencia sobre masas a la influencia dirigida y personalizada de elementos clave previamente definidos como críticos para una estrategia de acción.

Finalmente, hay un campo en el mundo de la psicología que tiene puntos en común con la radicalización de un individuo de especial interés para la creación de los diferentes relatos e informaciones a inyectar. Asimismo, y para la parte defensiva, el mundo de la psicología tiene mucho que aplicar para que puedan identificarse ataques como el planteado y poder tomar medidas preventivas. El concepto de “Guardaespaldas Virtual” toma sentido en un entorno como el que se plantea como forma de protección de los individuos frente a este tipo de ataques.

En esta mesa redonda se plantearán conceptos sobre este tema como punto de discusión para el posible desarrollo de estrategias y herramientas tanto ofensivas como defensivas en este campo de influencia sobre individuos.

Datos de la mesa redonda

Fecha: 7 de mayo – Hora: de 18:00 a 20:00 horas – Lugar: Sede de ACAMI

18:00 Palabras de bienvenida

GE R. D. Jaime Domínguez Buj – Presidente de la Academia de las Ciencias y las Artes Militares

18:10  Ponencia “La desinformación un instrumento clave en los conflictos actuales”

GB R. Dr. Miguel Ángel Ballesteros Martín – ACAMI

18:30   Ponencia “Así somos, así nos influyen”

Comandante Psicólogo Dña. Lucía Pery Pardo De Donlebún – EMAD

18:50 Ponencia “Caso práctico: Poniendo los huevos en la cesta”

Prof. Dr. Octavio Nieto-Taladriz García – Catedrático de Universidad en el Departamento de Ingeniería Electrónica de la E.T.S.I. de Telecomunicación – Universidad Politécnica de Madrid 

Prof. Dr. María Paz García Vera – Catedrática de Psicología Clínica en el Departamento de Personalidad, Evaluación y Psicología Clínica – Universidad Complutense de Madrid

19:30 PREGUNTAS

20:00 CLAUSURA

TFM: Design of a Communication System Through the Body
Posted on by rookie

The loss of a limb is a traumatic event for a human being, permanently altering the way they perform everyday tasks. Currently, most of these patients require a prosthesis for both aesthetic and functional reasons. Today, there are various types of prostheses, with robotic arms being the most commonly used for movement. These mechanical and/or electrical devices mimic human movements, controlled by the person. At present, the communication between the robotic arm and the user is established either through implants inside the body or via vulnerable communication methods.

The objective of this master’s thesis is to design a non-invasive communication system that uses the human body as a transmission medium. This approach is based on the innovative Human Body Communication (HBC) technology, which is part of Wireless Body Area Networks (WBAN). It is designed for wearable devices on the surface or inside the human body, specifically in the field of medicine. The goal is to transmit electrical or electromagnetic signals using the conductive properties of the human body.

To achieve this, an exhaustive study was conducted to understand how the human body behaves when a signal is transmitted at the selected frequency of 2.45 GHz. The signal will be transmitted through the patient’s forearm, which consists of multiple layers of materials with different dielectric properties. Therefore, computational simulations are necessary to analyze how the signal behaves.

This project is based on two experimental studies aimed at measuring propagation losses. The goal is to place the transmission and reception devices on the skin’s surface, using study [1] as a reference to calculate the signal losses through the multiple layers of the spleen. Additionally, the signal losses associated with transmission through the interior of the forearm, between the transmitter and receiver, were evaluated based on the data from study [2].

Once the system requirements were established, preliminary tests were conducted to validate the designed system. The results showed greater propagation losses than the theoretical estimates, prompting the project to focus on developing a functional prototype that is small, low-cost, and energy-efficient. The following image shows the completed system.

Finally, after testing the assembled system, it was determined that the selected insulator, RFSW-S-125-FR-PSA from Laird Technologies, is effective for communication through the air. However, aluminum yielded better results for communication through the body. On the other hand, the selected antenna was not ideal due to market limitations.

The results obtained suggest multiple areas for improvement and encourage further research to optimize the system.

References:

[1] Y. M. G. M. D. Zhi Ying Chen, «Propagation characteristics of electromagnetic wave on multiple tissue interfaces in wireless deep implant communication,» IET Microwaves, Antennas & Propagation, vol. 12, nº 13, pp. 2034-2040, 2018.

[2] C. G.-P. A. F.-L. A. V.-L. G. V. J. S. M. I. I. B. S. M. I. a. N. C. S. M. I. Ra´ul Ch´avez-Santiago, «Experimental Path Loss Models for In-Body Communications Within 2.36–2.5 GHz,» IEEE JOURNAL OF BIOMEDICAL AND HEALTH INFORMATICS, vol. 19, nº 3, pp. 930-937, 2015.

TFM: Design and implementation of a simulation environment for transcranial magnetic stimulation in human and mouse brains.
Posted on by rookie

The study of the human brain is currently a fundamental area of interest in science due to the complexity and diversity of functions performed by this organ. Although the brains of humans and mice differ in size and structure, they share numerous fundamental principles that allow scientists to extrapolate findings from rodent studies to humans. However, neuroscience research faces significant challenges due to the intrinsic complexity of nervous systems and the ethical and practical limitations associated with direct experiments on living organisms.

In this context, simulation environments have emerged as powerful tools for research. These environments allow for the modelling and detailed analysis of neural processes in a controlled setting without involving any living organisms. The ability to simulate brain activity when stimulated by external factors not only facilitates understanding of the brain’s response to these stimuli but also can accelerate the development of treatments for neurological diseases, such as cancer or stroke.

The main objective of this work is to develop a simulator capable of stimulating human and mouse brains using the transcranial magnetic stimulation method and quantifying the impact of various parameters in the simulation.

To achieve this objective, various brain simulators currently in use have been analysed, and one has been selected as the basis for the simulator. Additionally, the functioning of transcranial magnetic stimulation and the necessary instruments for carrying out this stimulation method have been studied. Furthermore, the modelling of the magnetic field generated by coils, both with and without a core, has been explored.

After gathering all this information, the simulator was completed, capable of simulating both human and mouse brains. Moreover, it allows for generating stimuli in the target brain with fully customized coils, as it is possible to model them by varying parameters such as height, radius, or number of turns. The intensity circulating through these coils can also be adjusted. Additionally, various commercial coils and stimulation systems consisting of multiple coils were successfully modelled.

Finally, various tests were conducted to verify that the modelling of the different coils was accurate and to measure different parameters. The parameters measured included the maximum radial electric field generated in the brain for each coil, the value of this electric field at different depths, the effect of the distance between the skull and the coil on the stimulation, and the field generated by the stimulation systems. Subsequently, all these tests were parametrized.

This project has developed and implemented a simulator capable of replicating brain stimulation in humans and mice through transcranial magnetic stimulation. The simulator allows customization of parameters such as coil position and number, distance from the skull, or stimulation intensity. After various tests, its accuracy has been confirmed, helping to reduce risks and improve personalized TMS treatments. Additionally, the inclusion of mouse models reduces the need for live experiments. The simulator offers applications in neuroscience research, therapy optimization, and the development of new clinical protocols.

Therefore, it can be confirmed that the proposed general objectives have been achieved and the technical feasibility of the project has been demonstrated.

All the code corresponding to the simulator is located in the following repository: https://github.com/rfparra/TFM