1. 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

2. Shannon, 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)

3. Information is carried out by : 1
Information is carried out by : 1. Amplitude and waveform of evoked activity
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

4. Information Processing
Cell Assemblies/Neuronal Networks

5. La actividad neuronal puede expresarse a través de diversas tecnologías
1. Registro de la actividad de campo cercano:
- Potenciales Provocados
- Potenciales Provocados de campo lejano
2. Descargas neuronales:
- con registros intracelulares
- con registros extracelulares
3. Magnetoencefalografía (MEG) Actividad provocada
4. Resonancia Magnética Funcional (fMRI)
5. Tomografía por Emisión de Positrones (PET)

6. Averaged Human Auditory Evoked Potentials
Wakefulness
B. Sleep
El sistema Auditivo Funciona 24 horas.
García-Austt et al

7. Auditory nerve compound action potentials HABITUATION
Buño, Velluti, Handler, García-Austt, 1966

8. Vía Auditiva Ascendente

9. Vía Auditiva Descendente (Eferente)

10. Cochlear nucleus post-stimulus time histograms

11. Histogramas Post Estímulos

12. Cortical Auditory Evoked Potentials in Rat
Hall and Borbély, 1970

13. Local-field and Far-field auditory evoked potentials
Velluti 2008
Velluti, Galambos

14. Guerit 1993

15. Tumor de Fosa Posterior derecha, Bulbo y Protuberancia
Guerit, 1993

16. Potenciales 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 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

18. 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

19. Auditory Cortex fMRI (Portas et al. 2005)

20. Magnetoencephalography
Cortical Auditory Evoked Activity
Kakigi et al. 2003

21. Redes Neuronales, Sueño y Audición
Getting 1989
MAGNETOENCEPHALOGRAPHIC EVOKED ACTIVITY
Kakigi et al. Sleep Med. (2003)

22. Cortical auditory units
Pre-Optic Region Unit
Cortical auditory units
McGinty 2005
Peña et al. 1999; Velluti, 2005

24. Events - related potentials to words
Bastuji and García-Larrea, 2005

25. Wave P300
Wakefulness
Sleep stages
Bastuji, Garcia-Larrea 2005

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).

27. Extracellular recording system during
Wakefulness and Sleep
Guinea pig partially restrained ready for
recording

28. Auditory Cortical (A1) Neuron
Velluti, Peña, Pedemonte, 2000

29. Cortical influences on Inferior Colliculus Auditory Neuron
Goldstein-Daruech,
Pedemonte, Inderkum, Velluti
Hearing Res. 2002

30. Normal and Inverted Guinea Pig Natural Call Stimuli
Auditory Cortical (A1) Recording
Pérez-Perera, Velluti. Actas de Fisiología 2001

31. Actividad Neuronal Unitaria Intracelular
Inferior Colliculus Auditory Neuron

32. Functional 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 field
A brief pulse of radio waves provide energy then the nuclei emit radio waves
The resonating nuclei thus became radio waves transmitters
The frequency of the radio waves is different in different chemical or physical environment

33. Positron Emission Tomography (PET) Imaging of Brain Activity
A radioactive solution is introduced into the bloodstream
The radioactive substance emit positrons (electrons positively charged) producing photons of light
Neurons normally use glucose in their metabolism. The 2-deoxyglucose is taken and its amount is proportional to their acyivity
Thus, the number of positron emissions indicate the neuron´s level of activity
Limitations: spatial resolution is only 5-10 mm; takes from 1 to many minutes to obtain; shows the activity of many thousands of neurons

34. Phrenology (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 modules
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.
…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.