Presentation on theme: "Actividad neuronal en el sistema auditivo: potenciales provocados y unidades Prof. Ricardo A. Velluti MD, DSc Neuro-Otología Experimental y Sueño Otorrinolaringología."— Presentation transcript:
Actividad neuronal en el sistema auditivo: potenciales provocados y unidades Prof. Ricardo A. Velluti MD, DSc Neuro-Otología Experimental y Sueño Otorrinolaringología (ORL), Hospital de Clínicas Programa de Desarrollo de Ciencias Básicas (Pedeciba) y ANII. Universidad de la República. Montevideo, Uruguay
Shannon, 1948; 1949 I nformation theory makes sense only if the receiver of signals knows the full range of possibilities. (Information transmitted in Morse code can be usefull only if the receiver knows that code)
Information is carried out by : 1. Amplitude and waveform of evoked activity 2. Neuronal firing rate (how the brain can measure the firing rate? 2. Neuronal firing rate (how the brain can measure the firing rate? 3. A response to a transient stimulus my be carried out by the first spike or two 4. Temporal distribution of the neuronal firing, pattern of discharge 5. Relationships with other brain rhythms
Information Processing Cell Assemblies/Neuronal Networks
La actividad neuronal puede expresarse a través de diversas tecnologías 1. Registro de la actividad de campo cercano:1. Registro de la actividad de campo cercano: - Potenciales Provocados - Potenciales Provocados - Potenciales Provocados de campo lejano - Potenciales Provocados de campo lejano 2. Descargas neuronales:2. Descargas neuronales: - con registros intracelulares - con registros intracelulares - con registros extracelulares - con registros extracelulares 3. Magnetoencefalografía (MEG) Actividad provocada3. Magnetoencefalografía (MEG) Actividad provocada 4. Resonancia Magnética Funcional (fMRI)4. Resonancia Magnética Funcional (fMRI) 5. Tomografía por Emisión de Positrones (PET)5. Tomografía por Emisión de Positrones (PET)
Averaged Human Auditory Evoked Potentials A.Wakefulness B. Sleep García-Austt et al El sistema Auditivo Funciona 24 horas.
Tumor de Fosa Posterior derecha, Bulbo y Protuberancia Guerit, 1993
Potenciales Provocados de Tronco Cerebral Muerte cerebral Chiappa 1997
…but the brain is also able to be in different states – called asleep, awake, or dreaming – involving changes like receiving sensory information that are not necessarily structural, rather functional. Thus, it is still possible that learning mechanisms are ascribed to the dynamic, emergent properties of neural ensembles. We have more neurons than proteins, and perhaps the former can carry out a good job without the need of any structural modifications of their already sophisticated connectivity. Why, then, do most neuroscientists prefer to lean on neural plasticity rather than on neural functional states? J.M. Delgado García, 2008 In: Velluti, 2008 The Auditory System in Sleep, pp
A HUB neuron: In adults tends to inhibit the activity of the recipient neuron, though in developing networks, GABA has excitatory effects. They also have very extensive axonal arborisations – they project over larger distances and make a greater number of and stronger synaptic connections than non-hub neurons. Finally, they are also more responsive to inputs and quicker to fire action potentials themselves, placing them in a position to orchestrate the responses of the entire network. Though hub neurons have so far only been observed in the hippocampus it seems almost certain that they will also be found in the cortex, where their effects may be fundamental for the information processing capabilities of the brain. Bonifazi, P., Goldin, M., Picardo, M., Jorquera, I., Cattani, A., Bianconi, G., Represa, A., Ben-Ari, Y., &Cossart, R. (2009). GABAergic Hub Neurons Orchestrate Synchrony in Developing Hippocampal Networks Science, 326 (5958), DOI
Auditory Cortex fMRI (Portas et al. 2005)
Magnetoencephalography Cortical Auditory Evoked Activity Kakigi et al. 2003
Redes Neuronales, Sueño y Audición MAGNETOENCEPHALOGRAPHIC EVOKED ACTIVITY Kakigi et al. Sleep Med. (2003) Getting 1989
McGinty 2005 Peña et al. 1999; Velluti, 2005 Pre-Optic Region Unit Cortical auditory units
Events - related potentials to words Bastuji and García-Larrea, 2005
Mismatch Negativity (MMN) MMN is a negative potential appearing between 100 and 200 ms as a consequence of any variation in a repetitive stream of stimuli. Its generators are in the superior temporal plane of the auditory cortex (review, Alho et al., 1995) with the addition of a frontal component (Giard et al., 1990).
Extracellular recording system during Wakefulness and Sleep Guinea pig partially restrained ready for recording
Functional Magnetic Resonance Imaging (fMRI) 1.When elements as the Hydrogen is exposed to a strong static magnetic field, the nuclei develop a net alignement in the direction of the applied field 2.A brief pulse of radio waves provide energy then the nuclei emit radio waves 3.The resonating nuclei thus became radio waves transmitters 4.The frequency of the radio waves is different in different chemical or physical environment
Positron Emission Tomography (PET) Imaging of Brain Activity 1.A radioactive solution is introduced into the bloodstream 2.The radioactive substance emit positrons (electrons positively charged) producing photons of light 3.Neurons normally use glucose in their metabolism. The 2- deoxyglucose is taken and its amount is proportional to their acyivity 4.Thus, the number of positron emissions indicate the neuron´s level of activity 5.Limitations: spatial resolution is only 5-10 mm; takes from 1 to many minutes to obtain; shows the activity of many thousands of neurons
Phrenology (Gall 1792) 1.Phrenology is based on the concept that the brain is the organ of the mind, and that certain brain areas have localized, specific functions or modulesbrainmindfunctions 2.2.Phrenologists believed that the mind has a set of different mental faculties, with each particular faculty represented in a different area of the brain.mental faculties 3.…so that a person's capacity for a given personality trait could be determined simply by measuring the area of the skull that overlies the corresponding area of the brain.