Transcript Timing of Neural Events - bio

Timing of Neural Events
Implications for Consciousness and Binding
By Jay Gunkelman, QEEG-Diplomate
QEEGJay @ SBCGlobal.net
www.QProWorldwide.com
Mind-Brain-Consciousness
Any respectable Model must explain memory (both semantic
and episodic), as well as “intention”, “attention”, Perception,
“awareness”, “discrimination”, and “conscious awareness”,
and predict whether a brain is conscious or not...
Objectively... and show a method of binding spatially
divergent areas of brain function into instantly functioning
interlaced neural networks... On both hemispheres.
The Model must use modern neuroscience, but be classically
based and be generally understandable by the nonspecialist (a criteria set by Wilder Penfield’s Mystery of the
Mind).
Memory
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Memory Storage is holonomic, and stored as a
distributed Gabor function (K. Pribram)
Semantic memory is enhanced by increased
higher frequency (11-13 Hz) thlamo-cortical
alpha content (environmental samples per
second) which is seen tonically in on-going
spindles.
Episodic memory is associated with a septohippocampal theta rhythm (Frontal Midline Theta;
FMT), which is seen phasically, in brief bursts.
For our “memory” to work, we need to have a relationship
between our short term episodic memory and our long term
memory. For detailed reference to EEG and memory, please see Klimesch’s work
on theta, alpha and memory.
ERP morphology can be created by an
instantaneous phase lock of alpha and theta
rhythms (Klimesch, 2004).
This time-series represents the interaction between
the limbic system’s phasic theta of the episodic
memory system and the thalamo-cortical
system’s semantic memory system, associated
with high frequency alpha components.
A mechanism for phase locking (synchronizing) of
the EEG needs to be identified...
BINDING
We have a complex set of brain functional
modules, and for us to be functional, we
need to have areas work together for one
task, and NOT to work together on
others.... For example, when a verbal
stimuli is given, and it has a semantic
unexpected difference, frontal lobe areas
evaluating the oddball semantic content
engage, while perceptual inputs are
attenuated parietally... Binding “in” and
blocking “out” neural networks... See the
ERPs:
ERP’s spatio-temporal domain: An “unexpected
semantic difference” elicits changes with a 400
milliseconds latency (D.Tucker, 1994)
Implications of timing on candidates for “Binding’s” mechanism.
Phase-locked gamma has been detected as early as 45
milliseconds in a cognitive task (Gurtubay et al, 2004) ... A
bit late to be the binding agent creating the network
for processing the data.
DC fields can mediate neuronal synchronization on a
time scale of one millisecond (E.R. John, 2005)
Mediation of the EEG’s synchrony by the DC field requires a field
gradient on the order of 100 uV/mm (Weaver, 1998).
DC field gradients of 100-200 uV/mm are seen in animals.
(Caton, R., 1875).
Perception is not continuous, but parsed into discrete
packets by thalamic gating, with sensory stimuli enhanced in the
negative phase and diminished in the positive phase of the alpha
wave, making 10 Hz alpha actually function as 10 samples per second
of the environment, with a 100 millisecond snapshot “frame”.
A “perceptual frame”, which is from 75 to 100 ms. (Efron, 1970) is
temporally quite similar to a “Micro-State” , which is 82 (+/- 4) ms
(D. Lehmann, et al., 2004).
The earliest components of ERPs correspond to
perceptual signal detection. The N1 occurs at 60-80 ms (thalamic
arrival), and P1 at about 100 ms (perceptual cortical arrival).
Initial sensory processing within the sensory
association cortex is noted from 90 to 130 ms.
The P2 is seen at about 200 milliseconds, and
correlates with sensory “awareness”, but not full
consciousness.
Stimulus detections posteriorly are
projected to prefrontal and parietal areas
from 130 to 280 ms (Halgren, et al., Cerebral Cortex 2002).
Phase-locked gamma activity appears between
the parietal and prefrontal cortex at approximately
180-230 ms in a cognitive task (Varela, 2000).
Posterior temporal phase-locked gamma is seen
at approximately 200 ms (Gurtubay, et al, 2004).
The P-300 has two components: The P3A is seen frontally at
225-250 ms, and the P3B appears parietally at 300-350 ms.
There is phase-locked gamma from 250-400 ms, found only
after the target stimuli (Gurtubay, et al., 2004).
The N400 is associated with “unexpected semantic
representation” (D. Tucker, 1994). The N450 is associated with
semantic encoding (Hillyard & Mangun, 1987).
The return of late evoked potential components is predictive of
recovery from coma (Alter, John, & Ransohoff, 1990), as are the presence of
“spindles” in coma... though many other EEG patterns in coma are either non-specific or offer
poor prognosis.
An ERP can be conceptualized as an approximation of one
cycle of the construction of a “frame” of consciousness.
Shifting attention volitionally shifts the ERP’s
cortical distribution
How many ERP cycles does it take to be
conscious??
When the second element of a pair of sensory
stimuli differs, an enhancement of the
amplitude of the ERP takes place. This DC
potential difference is considered a
measurement of attention, and is referred to
as “mismatch-negativity” (MMN).
ERPs in normal and ADHD
children in GO/NOGO task
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Amplitude of NOGO-GO difference
wave is higher in normal children
and depends of task performance in
ADHD children (12-14 years old).
The location of positive and
negative picks in the difference
wave remains the same for normal
and ADHD children.
Kropotov et al., in preparation
The MMN data shows that in a conscious person, the
recent past is continuously compared with the present,
thus suggesting that consciousness is the
remembered present. (Edelman (2001)
An “echoic memory trace” serially compares
events to a representation of the previous
event (Naatanen, 2004). This has a duration of
approximately 10 seconds, and is processed in
the dorsolateral prefrontal cortex. (E.R. John, 2005).
The implication is that consciousness requires two
ERP “perceptual cycles”: one to perceive, and another
to compare to the recalled present.
Conscious awareness of an event is delayed
about 500 ms, but this awareness is referred
backward to the ‘event-stream’ onset (Libet 1979).
This leaves us with the problem of “Binding”,
and the implications of these observations of
neural timing on the mechanisms capable of
binding a spatially diverse neural network...
“instantly”
The only system fast enough for spatially
distant neural network “phase binding” is the
millisecond time frame of the DC field, not
Gamma. (Gunkelman, 2004)
Initiated by the DC field’s millisecond time
domain synchronization effect, we see a
bispectral relationship between Gamma and
DC Field activity in the EEG... during
consciousness.
Gamma back-propagation and network phase
locking ‘resonance’ is generated after a
network is bound (John, 2005). (emphasis mine)
The resonant DC fields and phase locked EEG
rhythms yield consciousness, from within their
“nested rhythms”.
Nesting of frequencies constitutes a quantum
effect observed in the EEG (J. Pop-Jordanov, 2004).
Model summary:
Consciousness is an emergent property,
spawned from of the interaction between
1) DC fields, in the realm of the mind, and
2) EEG rhythms, in the realm of the brain...
When mind and brain interact, with quantum
nesting of rhythms... consciousness emerges.
Consciousness is not alchemy... It is based
solidly in modern neuroscience!
Decrease of beta and Gamma synchrony in ADHD
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Normal is compared with ADHD,
divided into high and low
performance subgroups.
“Go” stimuli elicited activity in
beta (14-18 Hz) band.
The degree and latency of beta
synchronization varied with
performance.
The Gamma differences are
apparent, with less gamma
content associated with
performance decreases
Note the modulated 6 Hz
‘nesting’ of Gamma in normal
conscious function
Data from J.Kropotov, 2000
Bispectral data showing a locked neural network in parkinsonism
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Timing of Neural Events
Implications for Consciousness and Binding
Presented by:
Jay Gunkelman, QEEG-Diplomate
QEEGJay @ SBCGlobal.net
www.QProWorldwide.com