Transcript Modelo experimental de la actividad neuronal en el sistema auditivo

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
[email protected]
Shannon, 1948; 1949
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)
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
Information Processing
Cell Assemblies/Neuronal Networks
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)
Averaged Human Auditory Evoked Potentials
A. Wakefulness
B. Sleep
A
B
García-Austt et al. 1961
El sistema Auditivo
Funciona 24 horas.
Auditory nerve
compound
action potentials
HABITUATION
Buño, Velluti, Handler, García-Austt, 1966
Vía Auditiva Ascendente
Vía Auditiva Descendente (Eferente)
Cochlear nucleus post-stimulus time histograms
WAKEFULNESS
A
B
C
D
0
40 ms
Toneburst
Histogramas Post Estímulos
Cortical Auditory Evoked Potentials
in Rat
Hall and Fig
Borbély,
1970
5.4.
Local-field and Far-field auditory evoked
potentials
B
A
Acx
MG
IC
SO left
CN
SO right
20 V
1 ms
Velluti 2008
Velluti, Galambos 1967
Guerit 1993
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 135-136.
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), 1419-1424 DOI
Auditory Cortex fMRI
(Portas et al. 2005)
Magnetoencephalography
Cortical Auditory Evoked Activity
Kakigi et al. 2003
Redes Neuronales,
Sueño y Audición
Getting 1989
MAGNETOENCEPHALOGRAPHIC
EVOKED ACTIVITY
Kakigi et al. Sleep Med. (2003)
Pre-Optic Region Unit
Cortical auditory units
McGinty 2005
Peña et al. 1999; Velluti, 2005
Events - related potentials to words
Bastuji and García-Larrea, 2005
Wave P300
Wakefulness
Sleep stages
Bastuji, Garcia-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
Auditory Cortical (A1) Neuron
Velluti, Peña, Pedemonte, 2000
Cortical influences
on Inferior
Colliculus
Auditory Neuron
Goldstein-Daruech,
Pedemonte, Inderkum, Velluti
Hearing Res. 2002
Normal and Inverted Guinea Pig Natural Call Stimuli
Auditory Cortical (A1) Recording
Pérez-Perera, Velluti. Actas de Fisiología 2001
Actividad Neuronal Unitaria Intracelular
Inferior Colliculus Auditory Neuron
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 2deoxyglucose 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
modules
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.
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.