Contact

Juan Felipe Ramirez-Villegas

Address: Spemannstr. 38
72076 Tübingen
Room number: 234
Phone: +49 7071 601 1671
Fax: +49 7071 601 652
E-Mail: juan.ramirez-villegas

 

Picture of Ramirez-Villegas, Juan Felipe

Juan Felipe Ramirez-Villegas

Position: PhD Student  Unit: Logothetis

My core academic interests focus on:

  • Neural modeling / Neurodynamics
  • Non-linear systems
  • Physiology of memory and cortico-/subcortico-hippocampal interactions
  • Signal processing
  • Machine Learning

 

Currently, I am a doctoral candidate at the Max Planck Institute for Biological Cybernetics jointly under Dr. Michel Besserve and Prof. Nikos Logothetis. I analyse, model and develop analysis methods for multi-dimensional neural data in order to investigate the system-level mechanisms of cognitive processes such as memory encoding, transfer and consolidation. I have a special interest in unsupervised-learning methods for pattern analysis and representation of high-dimensional data.

 

Brain activity is precisely coordinated at multiple scales: from local networks of neurons (e.g. the recurrent CA1 circuitry in the hippocampus) and areas (e.g. the hippocampal formation) to all subcortical and neocortical brain domains. However, how these scales relate to each other remains an open scientific question. My main research focus has been to investigate this question under specific theoretical and experimental paradigms. In particular, I have studied the relationship between ongoing spontaneous neuronal activity in the hippocampus, brainstem and thalamic structures (such as the pontine region’s parabrachial nucleus and the lateral geniculate nucleus, respectively) at microscopic, mesoscopic and macroscopic scales by combining data from extracellular recordings and functional magnetic resonance imaging (fMRI). To this end, I investigate the neurophysiological underpinnings of neural events at the spatial and temporal scales offered by these experimental methodologies. These events manifest themselves as recurring episodes of deflection in the extracellular field potential, signalling cooperative microcircuit activities occurring on the basis of the state of the animal (wakefulness, slow-wave sleep and paradoxical sleep).

 

In order to cope with this highly multivariate multi-modal data, I develop and employ principled data analysis techniques based on statistical learning, signal processing and multi-variate statistics. In addition, I develop multi-compartmental (conductance-based) and mean-field network models in order to further understand the microcircuit dynamics that underlie physiological neural event-related activity, and these events in settings that simulate pathological conditions.

News (coming out in 2017)

 

--> Journal Articles

Ramirez-Villegas JF, Murayama Y, Evrard HC, Besserve M, Logothetis NK (2017) State-dependent transient control of hippocampus by pontogeniculooccipital (PGO) waves in the macaque brain. (in preparation)


Ramirez-Villegas JF, Willeke KF, Logothetis NK & Besserve M (2017) Investigation of the neuronal-ensemble mechanisms underlying sharp wave-ripples (submission due Sept 2017)

 

Ramirez-Villegas JF, Logothetis NK & Besserve M (2017) Growing neural gas and fast growing neural gas for cluster analysis of multi-dimensional brain signals (in preparation)

2012-2016           Eberhard-Karls Universität Tübingen                           Germany


Graduate School of Neural & Behavioral Sciences, IMPRS / Max Planck Institute for Biological Cybernetics, Dept. Logothetis

 

PhD in Neuroscience (Systems Neuroscience)


Doctoral thesis Advisor: Dr. Michel Besserve, Prof. Nikos K Logothetis

 

Thesis advisory board - Prof. Andreas Bartels (Eberhard-Karls University of Tübingen), Prof. Gustavo Deco (Universitat Pompeu Fabra), Prof. Nikos K. Logothetis (Max Planck Institute for Biological Cybernetics)


2009 Engineering Diploma Thesis                                                           Colombia


Heart rate variability dynamics for the prognosis of cardiovascular risk (Ramirez-Villegas et al., 2011)

 

2004-2009        Universidad Autonoma de Occidente                              Colombia


Diploma in Biomedical Engineering

 

Since 2012, I've concurrently acted as reviewer for the following journals (mainly in machine learning or processing of electrophysiological signals):

 

Journal reviewer for Elsevier’s Atherosclerosis

Journal reviewer for Elsevier’s Artificial Intelligence in Medicine

Journal reviewer for Elsevier’s Computer Methods and Programs in Biomedicine

Journal reviewer for Elsevier’s Computers in Biology and Medicine

Journal reviewer for IEEE Transactions on Instrumentation & Measurement

Journal reviewer for BioMedical Engineering Online

Journal reviewer for PLoS ONE

Journal reviewer for Elsevier’s Journal of Neuroscience Methods

Journal reviewer for Elsevier’s Computers and Electrical Engineering

Journal reviewer for Elsevier’s Biomedical Signal Processing and Control

Journal reviewer for Elsevier’s Expert Systems with Applications

Journal reviewer for International Journal of Bifurcation and Chaos

Journal reviewer for Springer’s Neural Computing and Applications

Journal reviewer for IEEE Journal of Biomedical and Health Informatics

 

If you have further interest on my research drop me a line via e-mail.

Logothetis NK , Murayama Y , Besserve M , Evrard H and Ramirez-Villegas J (November-16-2016) Abstract Talk: PGO wave-triggered functional MRI: mapping the networks underlying synaptic consolidation , 46th Annual Meeting of the Society for Neuroscience (Neuroscience 2016), San Diego, CA, USA(670.12) .
By combining concurrent electrophysiological recordings and fMRI, we recently demonstrated that the events known as hippocampal sharp wave-ripple complexes (SPW-R) are tightly associated with robust cortical activations that occur concurrently with a particularly intriguing strong inhibition of large portions of subcortical brain structures that are closely involved in neural plasticity, such as the basal ganglia (BG), the pontine region (PONS) and the cerebellar cortex (Logothetis, Eschenko et al. 2012, Nature 491:547-53). Particularly intriguing was the strong inhibition of large portions of subcortical brain structures that are closely involved in neural plasticity, such as the basal ganglia (BG), the PONS and the cerebellar cortex. In primates, the negative BOLD in the pontine region was systematically associated with inhibition of the lateral geniculate nucleus (LGN) and foveal V1 activity, despite the overall positive fMRI responses in peripheral V1 and all other primary sensory and associational cortices. The deactivation of PONS may therefore be due to a temporary suppression of cholinergic sites involved in local plasticity and synaptic consolidation, such as those underlying the generation-propagation of theta rhythm, and so-called ponto-geniculo-occipital (PGO) waves. PGO waves have been often associated with the consolidation of procedural memory or synaptic consolidation in general. To examine this hypothesis and better understand the global regulation of brain activity during memory consolidation we set out to employ the methodology of Neural-Event-Triggered fMRI (NET-fMRI), combining simultaneous electrophysiological recordings in the region of the parabrachial nucleus (PBn) and MR imaging in monkeys under opioid anesthesia. First, we established a structural-MRI and angiography-based site-localization approach to access various brainstem regions with long electrodes without potential complications due to vasculature-injury. We subsequently physiologically identified PBn, LGN and the Hippocampal CA1/CA3 fields, and conducted concurrent, uninterrupted multi-site physiological and fMRI recordings in a 4.7T magnet. PGO events were considered to be the large field deflections, with various temporal and repetition profiles that typically co-occur in PBn and LGN. In sharp contrast to isolated LGN or PONS events, the PGO-like events - co-occurring in both pontine and thalamic structures - yielded a robust and striking pattern of up/down modulation, suggesting the PGO events correlated with upregulation of subcortical centers concurrently with inhibition of activity in neocortex.
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Articles (7):

Ramirez-Villegas JF, Logothetis NK and Besserve M (November-2015) Diversity of sharp-wave–ripple LFP signatures reveals differentiated brain-wide dynamical events Proceedings of the National Academy of Sciences of the United States of America 112(46) E6379–E6387.
Ramirez-Moreno DF, Schwartz O and Ramirez-Villegas JF (April-2013) A saliency-based bottom-up visual attention model for dynamic scenes analysis Biological Cybernetics 107(2) 141-160.
Ramirez-Villegas JF and Ramirez-Moreno DF (February-2013) Color coding in the cortex: a modified approach to bottom-up visual attention Biological Cybernetics 107(1) 39-47.
Ramirez-Villegas JF and Ramirez-Moreno DF (February-2012) Wavelet packet energy, Tsallis entropy and statistical parameterization for support vector-based and neural-based classification of mammographic regions Neurocomputing 77(1) 82–100.
Ramirez-Moreno DF and Ramirez-Villegas JF (July-2011) Una implementación computacional de un modelo de atención visual Bottom-up aplicado a escenas naturales [A Computational Implementation of a Bottom-up Visual Attention Model Applied to Natural Scenes] Revista de Ingeniería 35 6-11.
Ramirez-Villegas JF, Lam-Espinosa E, Ramirez-Moreno DF, Calvo-Echeverry PC and Agredo-Rodriguez W (February-2011) Heart Rate Variability Dynamics for the Prognosis of Cardiovascular Risk PLoS ONE 6(2) 1-15.
Ramírez-Villegas JF and Ramírez-Moreno DF (July-2010) Una revisión de modelos de atención visual Bottom-up neurobiológicamente inspirados El Hombre y la Máquina 35 143-152.

Conference papers (1):

Ramírez-Villegas JF, Lam-Espinosa E and Ramírez-Moreno DF (October-2009) Microcalcification Detection in Mammograms Using Difference of Gaussians Filters and a Hybrid Feedforward-Kohonen Neural Network, XXII Brazilian Symposium on Computer Graphics and Image Processing (SIBGRAPI 2009), IEEE, Piscataway, NJ, USA, 186-193.

Contributions to books (1):

Ramirez-Villegas JF and Ramirez-Moreno DF: Microcalcification Detection in Digitized Mammograms: A Neurobiologically-Inspired Approach, 161-186. In: Digital Image Processing, (Ed) S.G. Stanciu, InTech, Rijeka, Croatia, (2011).

Posters (5):

Ramirez-Villegas JF, Logothetis NK and Besserve M (November-14-2016): Statistical source separation of rhythmic LFP patterns during sharp wave ripples in the macaque hippocampus, 46th Annual Meeting of the Society for Neuroscience (Neuroscience 2016), San Diego, CA, USA.
Ramirez-Villegas JF, Logothetis NK and Besserve M (December-2015): Sharp wave-ripple complexes in a reduced model of the hippocampal CA3-CA1 network of the macaque monkey, Twenty-Fourth Annual Computational Neuroscience Meeting (CNS*2015), Praha, Czech Republic, BMC Neuroscience, 16(Supplement 1) 24.
Ramirez-Villegas JF, Logothetis NK and Besserve M (October-19-2015): Diversity of sharp wave-ripples in the CA1 of the macaque hippocampus and their brain wide signatures, 45th Annual Meeting of the Society for Neuroscience (Neuroscience 2015), Chicago, IL, USA.
Ramirez-Villegas JF, Logothetis NK and Besserve M (September-3-2014): Dynamical source analysis of hippocampal sharp-wave ripple episodes, Bernstein Conference 2014, Göttingen, Germany.
Ramirez-Villegas JF, Logothetis NK and Besserve M (March-2014): Cluster analysis of sharp-wave ripple field potential signatures in the macaque hippocampus, Computational and Systems Neuroscience Meeting (COSYNE 2014), Salt Lake City, UT, USA.

Talks (1):

Logothetis NK, Murayama Y, Ramirez-Villegas J, Besserve M and Evrard H (November-16-2016) Abstract Talk: PGO wave-triggered functional MRI: mapping the networks underlying synaptic consolidation, 46th Annual Meeting of the Society for Neuroscience (Neuroscience 2016), San Diego, CA, USA(670.12).

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Last updated: Monday, 22.05.2017