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This presentation discusses in detail the transients that occur mainly in late stage 1 and stage 2 of sleep, and may be confused to be pathological. The prototype here are theK complexes and the Sleep Spindles.
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Electroencephalogram, Spindles and K complexes
Sleep
• The default state
• Active Process
• Requires synchronizers
• Sleep Spindles, K Complexes
Raphe promotes sleep
Locus coeruleus promotes wakefulness
*so sleep control is distributed across centers
The reticular formation also promotes wakefulness
Slow-Wave Activity: -- Spindles: 7 - 15 Hz ; Wax and Wane -- Delta: 1 - 4 Hz -- Slow Osc. .5 - 1 Hz
Stages of sleep form cyclical pattern
Sleep Spindles
• Compared to alpha rhythm !!
• One of the earliest described events
• Hallmark of Synchronization
• Requires an oscillator
Klimesch VO: BioIII 7
The approximate location of the three cuts for the human brain areshown below.
Thalamus
Cerebellum
Encephale isole‘
Midpontine pre- trigeminal
Cerveau isole‘
Norm
al sle
ep-w
ake
cycle
i nc lu
di n
g R
EM
SW
S
Sle
ep-w
ake
c ycl e
with
out R
EM
THALAMUS
REVA
A
M
VL
VP LP
LGN
MGN
Pu
G. prae-centralis
G. post-centralis
Gyri frontales
Gyri orbitales
Gyritemporales
Gyriparietales
Corpus striatum
Thalamocortical Network
Ctx
RE TC+
+
+
-
Thalamocortical spindle circuitry
Modified from Steriade and Llinás. Physiol.Rev. 68:649-742, 1998.
T type calcium channel genes in thalamus
Courtesy of E Talley, D Bayliss & E Perez-Reyes
1H
1G
1I
Post inhibitory rebound in thalamic relay neurons
Vm
hT
-60
-70
-80
1
0
100 ms
IPSP
T channels reprimed
Ca2+-depende
nt rebound
burst
threshold
Th-cx
Th-cx
L-circ
L-circRE
RE
Aff
Dendro-dendr.
Cortex
Thalamo-cortical reentrant loops. Steriade, M. (1999). Coherent oscillations and
short-term plasticity in corticothalamic networks. TINS, Vol. 22 (8), 337-344.
Basic Circuitry:
Cortex
RE Dorsal Thal. = Relay Nuclei
‚Secondary neurons‘
Th-cx
Th-cx
L-circ
L-circ
RE
RE
Aff
Dendro-dendr.
Cortex
1,2 Afferent brainstem input to Th-cx (1), Activation of RE and Cortex (2)
Th-cx
Th-cx
L-circ
L-circ
RE
RE
Aff
Dendro-dendr.
Cortex
3 Excitatory processes in Cortex; Inhibition of primary L-circ; Inhibition of other RE cells
Th-cx
Th-cx
L-circ
L-circRE
RE
Aff
Cortex
The resulting effect is that during time 4, Th-cx are again under inhibitory control from L-circ neurons and, at the same time are activated from cortico-thalamic cells. Thus, only strong (converging and/or amplified) cortical feedback will trigger another excitatory activation wave into the cortex in time 5.
4 Excitatory feedback response from cortex. Disinhibition of primary L-circ neurons. Inhibition of secondary Th-cx neurons.
The strong inhibition of the secondary Th-cx
cell may lead to low threshold spikes
(LTS) and, thus, to a 10 Hz oscillation.
Th-cx
Th-cx
L-circ
L-circRE
RE
Aff
Cortex
5 The primary Th-cx cell may start a new excitatory burst into the cortex. At this stage (because released from the L-circ inhibition), a new afferent input will have a strong effect.
The secondary Th-cx cells remain under inhibition
RESULT: Center-surround ‚on-off‘ effect with a resulting strong focal activation of cortical target neurons.
Summary of findings: Afferent brainstem activation is missing and cortical activation is strong:
- Th-cx cells are hyperpolarized and oscillate with spindle frequency Note that a depol. current pulse during maximal hyperpol. leads to high frequency bursts. The result is increased oscillatory cortical activation leading to Delta activity.- The effect of increased cortical activation is even larger if stimulation patterns are oscillatory
Th-cxL-circ
RE
Missing brainstem afferents
Cortex Th-cx hyperpolarized,Sleep spindles
SLEEP: Spindles and Delta
Spindle oscillations in thalamus
A M PA /N M D A R
G A BA RA
TC
nR t
-
+
Thalam us
C ortex
IPSP
Rebound Burst
EPSP & Burst
200 m s
20 m
V
timing
RE Cell Rapidly bursting type
A Mathematical model
Foundations II - Neuroimaging
TC Cell modulation by RE cell
A Mathematical model
Propagation of Spindles
Ontogeny of Spindles
• EEG maturation
• Posterior Dominant
• Anterior spread
• Amplitude decreases with age
• Two ditinct frequency bands seen
K Complexes
Paroxysmal Events
K Complexes
• stage 2 sleep, arousing stimuli. • Loomis et al. (1938); • reason for calling them K complexes remains
obscure • spur of the moment • Knocking
• K complex shows a maximum over the vertex, • also K complexes with an indubitable
maximum over the frontal midline.
• H. Davis et al. - central and frontal K complexes
• Brazier (1949) presumed two distinct generators; these were area 6, corresponding with the vertex, and area 9, corresponding with frontal midline.
• initial sharp component, followed by a slow component that fuses with a superimposed fast component.
• The sharp component is biphasic and not seldom multiphasic.
• The slow component is represented by a large slow wave that may exceed 1,000 msec in duration
POSTS start to occur in healthy people at age 4 years, become fairly common by age 15 years, remain common through age 35 years, and start to disappear by age 50 years.
POSTS are seen very commonly on EEG and have been said to be more common during daytime naps than during nocturnal sleep.
Most characteristics of POSTS are contained in their name. They have a positive maximum at the occiput, are contoured sharply, and occur in early sleep (stages I and II). Their morphology classically is described as "reverse check mark," and their amplitude is 50-100 V. They typically occur in runs of 4-5 Hz and are bisynchronous, although they may be asymmetric. They persist in stage II sleep but usually disappear in subsequent stag
Positive occipital sharp transients of sleep
Also called vertex waves or V waves, these transients are almost universal. Although they often are grouped together with K complexes, strictly speaking, vertex sharp transients are distinct from K complexes. Like K complexes, vertex waves are maximum at the vertex (central midline placement of electrodes [Cz]), so that, depending on the montage, they may be seen on both sides, usually symmetrically. Their amplitude is 50-150 V. They can be contoured sharply and occur in repetitive runs, especially in children. They persist in stage II sleep but usually disappear in subsequent stages. Unlike K complexes, vertex waves are narrower and more focal and by themselves do not define stage II.
Vertex sharp transients