Presentation on theme: "Prof. Ricardo A. Velluti MD, DSc Neuro-Otología Experimental y Sueño"— Presentation transcript:
1Actividad neuronal en el sistema auditivo: potenciales provocados y unidades Prof. Ricardo A. Velluti MD, DScNeuro-Otología Experimental y SueñoOtorrinolaringología (ORL), Hospital de ClínicasPrograma de Desarrollo de Ciencias Básicas (Pedeciba) y ANII. Universidad de la República. Montevideo, Uruguay
2Shannon, 1948; Information 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)
3Information is carried out by : 1 Information is carried out by : 1. Amplitude and waveform of evoked activity2. 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 two4. Temporal distribution of the neuronal firing, pattern of discharge5. Relationships with other brain rhythms
5La actividad neuronal puede expresarse a través de diversas tecnologías 1. Registro de la actividad de campo cercano:- Potenciales Provocados- Potenciales Provocados de campo lejano2. Descargas neuronales:- con registros intracelulares- con registros extracelulares3. Magnetoencefalografía (MEG) Actividad provocada4. Resonancia Magnética Funcional (fMRI)5. Tomografía por Emisión de Positrones (PET)
6Averaged Human Auditory Evoked Potentials WakefulnessB. SleepEl sistema Auditivo Funciona 24 horas.García-Austt et al
15Tumor de Fosa Posterior derecha, Bulbo y Protuberancia Guerit, 1993
16Potenciales Provocados de Tronco Cerebral Muerte cerebral Chiappa 1997
17…but the brain is also able to be in different states – called asleep, awake, or dreaming – involving changes like receiving sensoryinformation that are not necessarily structural, ratherfunctional.Thus, it is still possible that learning mechanismsare ascribed to the dynamic, emergent properties of neuralensembles. We have more neurons than proteins, and perhapsthe former can carry out a good job without the need of anystructural modifications of their already sophisticated connectivity.Why, then, do most neuroscientists prefer to lean onneural plasticity rather than on neural functional states?J.M. Delgado García, 2008In: Velluti, 2008 The Auditory System in Sleep, pp
18A 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
26“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).
27Extracellular recording system during Wakefulness and SleepGuinea pig partially restrained ready forrecording
32Functional Magnetic Resonance Imaging (fMRI) 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 fieldA brief pulse of radio waves provide energy then the nuclei emit radio wavesThe resonating nuclei thus became radio waves transmittersThe frequency of the radio waves is different in different chemical or physical environment
33Positron Emission Tomography (PET) Imaging of Brain Activity A radioactive solution is introduced into the bloodstreamThe radioactive substance emit positrons (electrons positively charged) producing photons of lightNeurons normally use glucose in their metabolism. The 2-deoxyglucose is taken and its amount is proportional to their acyivityThus, the number of positron emissions indicate the neuron´s level of activityLimitations: spatial resolution is only 5-10 mm; takes from 1 to many minutes to obtain; shows the activity of many thousands of neurons
34Phrenology (Gall 1792)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 modules2.Phrenologists believed that the mind has a set of different mental faculties, with each particular faculty represented in a different area of the brain.…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.