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
  • Biological visual processing

 

I am a PhD student at the Max Planck Institute for Biological Cybernetics under Dr. Michel Besserve and Prof. Nikos Logothetis. I analyze, model and develop analysis methods for multi-dimensional neural data. 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 (such as the recurrent hippocampal CA1 circuitry) and areas (such as the hippocampal formation) to all subcortical and neocortical brain domains. However, how these scales relate to each other remains an open scientific question. One of my main research focuses is to investigate this question under specific theoretical and experimental paradigms. In particular, I study the relation between ongoing spontaneous neuronal activity in the hippocampus at meso- and macroscopic scales by combining extracellular recordings and functional magnetic resonance imaging (fMRI) (see Logothetis et al., Nature, 2012).

 

In my doctoral project, I am characterizing and modeling spontaneous transitions of neuronal activity in the hippocampus. Specifically, I am interested in the mechanisms underlying the occurrence and dynamics of sharp-wave ripple (SPW-R) complexes: Network release phenomena observed in the LFP of the hippocampal CA1 subfield, due to aperiodic reduction of theta-like inhibition from MS/DB (namely, medial septum-diagonal band of Broca) in CA3. These episodes are central to the reactivation of memory traces. Notably, SPW-R-related activity can be biased by parahippocampal, neocortical and long-range neuromodulatory inputs. Thus, I aim at understanding how these multi-structure and network interactions -at play during SPW-Rs- support cognitive demands, possibly establishing a frame not only for selective consolidation, but also for memory recall during awake state (see also Ramirez-Villegas et al., PNAS, 2015).

News (coming out in 2015/2016)

 

--> Journal Articles

Ramirez-Villegas JF, Logothetis NK & Besserve M (2015) Diversity of sharp wave-ripple complexes reveals differentiated brain-wide dynamical events. Proceedings of the National Academy of Sciences of the USA 112(46), pp. E6379-E6387

 

Ramirez-Villegas JF, Murayama Y, Logothetis NK & Besserve M (2016) Ponto-geniculo-occipital waves in the macaque brain ... (in preparation - title TBA)


Ramirez-Villegas JF, Logothetis NK & Besserve M (2016) Decomposition of LFP into rhythmic components reveals neuronal-ensemble mechanisms of hippocampal sharp wave-ripples (under review)

 

Ramirez-Villegas JF, Logothetis NK & Besserve M (2016) A minimal multi-compartment model of the macaque CA3-CA1 network predicts hippocampal ripple episodes dynamics (in preparation)

 

Ramirez-Villegas JF, Logothetis NK & Besserve M (2016) Growing neural gas and fast growing neural gas for cluster analysis of multi-dimensional brain signals (in preparation)

 

--> Commentary/Review

Ramirez-Villegas JF & Besserve M (2016) Sharp wave-ripples and hippocampal-cortical dialogue in the primate brain.

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 (Doktorvater)

 

Thesis advisory board - Dr. Andreas Bartels (Eberhard-Karls University of Tübingen), Prof. Stefano Panzeri  (Italian Institute of Technology), 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:

 

Elsevier’s Atherosclerosis

Elsevier’s Artificial Intelligence in Medicine

Elsevier’s Computer Methods and Programs in Biomedicine

Elsevier’s Computers in Biology and Medicine

IEEE Transactions on Instrumentation & Measurement

BioMedical Engineering Online

PLoS ONE

Elsevier’s Journal of Neuroscience Methods

Elsevier’s Computers and Electrical Engineering

Elsevier’s Biomedical Signal Processing and Control

International Journal of Bifurcation and Chaos

Springer’s Neural Computing and Applications

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