Above hypothalamus is golf-ball-sized ellipsoidal region {thalamus}|.
functions
Thalamus is for attention, respiration, short-term memory, and long-term memory. It can detect sensations, temperature, pain, and moderate skin stimulation. It identifies objects and initiates avoidance behavior. In mammals and humans, it directs attention to language. It affects autonomic system.
Thalamus has feeding center that controls eating behavior. It has satiety center that has glucose receptors.
anatomy
Ventral reticular nucleus is thin shell that surrounds walnut-sized dorsal thalamus. Thalamus has few intrinsic neurons.
anatomy: nuclei
Thalamic nuclei include anterior, centromedian, dorsolateral, dorsomedial, intralaminar, lateral geniculate for vision, medial geniculate for audition, multimodal, pulvinar, reticular, ventral anterior, ventral lateral, ventral posterior, and ventrobasal complex for somatosensation [Jones and Peters, 1986] [Jones, 1985] [Sherman and Guillery, 2001].
input
Main inputs to cortex first pass through two dozen thalamus regions. Glomeruli and glia surround incoming sense-nerve axons. Thalamus has projection areas for skin regions, with subareas for touch, pressure, muscle, and joint movement. Thalamus has input neurons for taste and for taste and touch.
Number of cortical fibers projecting back to thalamic nuclei is much larger than number of fibers from senses to thalamus.
output
All nuclei have matrix cells with diffuse projections. Thalamus has as many outputs as inputs but has no axon collaterals.
Thalamus inhibits optic tectum in lower vertebrates.
Core relay neurons send to cortex layer 4. Matrix neurons send to cortex layers 1, 2, and 3. Clustered neurons {core neuron}, such as magnocellular and parvocellular neurons, excite layer 4 in small cortex regions. Other neurons, such as koniocellular neurons, send to layers 2 and 3 in larger cortical regions {matrix neuron} [Jones, 2002].
damage
Non-specific thalamus damage causes consciousness loss. Thalamic damage can cause sense or motor loss.
processing
Input causes one spike and then 100 milliseconds of inhibition. Thalamic neurons can replicate sense input or can burst in 30-Hz to 40-Hz pattern unrelated to input. Thalamus reticular nucleus can switch lateral geniculate nucleus into burst mode.
Limbic-system anterior-thalamus region {anterior thalamic nucleus} {anterior sensory thalamus} relays affective visceral information to cortex and controls ergotropic behavior through sympathetic nervous system.
Thalamic nucleus {centromedian nucleus} {centrum medianum nucleus} sends to cerebellum and corpus striatum.
Thalamic ganglia {dorsolateral thalamic nucleus} can send to parietal lobe.
A limbic-system part {dorsomedial thalamic nucleus} can receive from olfactory lobe and amygdala and send to frontal lobe and hypothalamus.
Lateral geniculate nucleus sends, through optic radiation {geniculostriate pathway, brain}, to occipital lobe visual cortex area V1. Geniculostriate and tectopulvinar pathways interact. Lateral geniculate nucleus damage causes poor acuity.
Thalamus medullary-laminae nuclei {intralaminar nuclei} {intralaminar complex} (ILN) {nucleus circularis} can have neurons organized in torus and include geniculate bodies. ILN surrounds medial dorsal nucleus. Other thalamic nuclei are principal nuclei.
purpose
Loops through striatum, pallidum, and thalamus underlie arousal and awareness.
input
Intralaminar nuclei receive from reticular formation for arousal, spinothalamic system for temperature and pain, trigeminal complex for temperature and pain, cerebellum dentate nuclei for proprioception, globus pallidus for motor feedback, periaqueductal gray for emotion, substantia nigra for emotion, amygdala for emotion, and vestibular nuclei for body position.
Laterodorsal tegmentum, peduncle, and pons cholinergic neurons excite excitatory thalamocortical-relay-neuron nicotinic receptors, and those cholinergic neurons inhibit inhibitory thalamic-reticular neuron muscarinic receptors, resulting in new excitation. Basal forebrain cholinergic and noradrenergic axons go to Layer I and to lower layers. Ventrobasal nucleus sends to Layer IV.
output
Intralaminar nuclei connect, with collaterals to nucleus reticularis, to striatum, pulvinar, all cortical layers 1 to 3, except visual cortex and inferotemporal cortex, and basal ganglia.
Intralaminar nucleus {centrum medianum} {entromedian nucleus} stains differently, is for will, and sends to motor cortex and striatum.
Intralaminar-nuclei matrix neurons can send to Layer I, to modulate lower layers. Intralaminar-nuclei core neurons can send mainly to Layer V and VI, to carry main signals.
damage
Strokes in thalamoperforating arteries {paramedian arteries} can damage both ILN. Both-side damage ends waking consciousness [Baars, 1995] [Bogen, 1995] [Cotterill, 1998] [Hunter and Jasper, 1949] [Kinney et al., 1994] [Koch, 1995] [Llinás and Paré, 1991] [Minamimoto and Kimura, 2002] [Newman, 1997] [Purpura and Schiff, 1997] [Schlag and Schlag-Rey, 1984].
Lateral geniculate nucleus has six separate cell layers, four parvocellular layers at top with small cells and two magnocellular layers at bottom with large cells. Between layers are cone-shaped cells {koniocellular neuron} that code for blue-yellow opponency, the difference between S cones and L+M cones [Calkins, 2000] [Chatterjee and Callaway, 2002] [Dacey, 1996] [Nathans, 1999].
Thin thalamic nuclei {lateral dorsal nucleus} can be in anterior, be for memory and emotion, and send to anterior cingulate gyrus.
Thalamus nucleus {lateral geniculate nucleus}| (LGN) is for object identification [Przybyszewski et al., 2000] [Shepherd, 1998] [Sherman and Guillery, 2001] [Sherman and Koch, 1998].
input
LGN receives from all senses except olfaction, especially from retinal ganglion neurons. It is sensitive to eye position. It has dermatomal segments to represent body sensations.
Thalamus receives much more feedback from cortex than it sends to cortex. Such positive and negative feedback probably applies learned and innate information to bias stimulation, which predicts stimuli [Koch, 1987] [Mumford, 1991] [Mumford, 1994] [Rao and Ballard, 1999].
LGN has circular receptive fields.
output
LGN sends, through optic radiation {geniculostriate pathway, vision}, to visual cortex area V1 in occipital lobe. Geniculostriate and tectopulvinar pathways interact.
LGN sends to somaesthetic cortex.
LGN sends to overlapping, multiple lateral geniculate nucleus cells {relay cell}. Through dendrodendritic connections, LGN affects neurons up to five millimeters away.
Neurons inhibit themselves.
damage
Damage to lateral geniculate causes poor acuity.
anatomy: layers
Lateral geniculate nucleus has six separate cell layers, four parvocellular layers at top with small cells and two magnocellular layers at bottom with large cells. Parvocellular and magnocellular core neurons send to one cortex region.
LGN layers 1, 4, and 6 are for opposite-side eye. Layers 2, 3, and 5 are for same-side eye. Layer 1 and 2 neurons respond to OFF, at any wavelength. Layer 3 and 4 neurons respond to ON or OFF, at wavelength range. Layer 5 and 6 neurons respond to ON, at wavelength range. Layer 3 and 4 neurons have opponent cells for red-green and blue-yellow.
anatomy: magnocellular
Magnocellular cells receive from bipolar cells with bigger dendrite trees and send transient signals to visual-cortex layer 4c-alpha and layer 6. These large cells are for temporal resolution, movement, and flicker. Optic-tract axons from right and left eyes synapse on separate magnocellular neurons, in bands.
anatomy: parvocellular
Parvocellular cells receive from midget cells and send sustained signals to visual-cortex layer 4cbeta. Small cells are for color, spatial resolution, texture, shape, depth perception, and stereopsis [Merigan and Maunsell, 1993] [Schiller and Logothetis, 1990].
anatomy: koniocellular
Between layers are koniocellular neurons {matrix cell} that code for blue-yellow opponency, the difference between S cones and L+M cones [Calkins, 2000] [Chatterjee and Callaway, 2002] [Dacey, 1996] [Nathans, 1999]. Koniocellular cells go to several regions.
anatomy: Y cells
Y cells maintain activity after moving object crosses receptive field, using cortico-thalamic feedback.
color processing
Brain has four opponent processes. Cell can react oppositely to red and green or green and red. Cell can react oppositely to blue and yellow or yellow and blue. Luminance is sum of red and green. Comparisons cross, so the three colors add orthogonally.
Magnocellular cells {magnocellular layer} receive from bipolar cells with bigger dendrite trees and send transient signals to visual-cortex layer 4c-alpha and layer 6. These large cells are for temporal resolution, movement, and flicker. Optic-tract axons from right and left eyes synapse on separate magnocellular neurons, in bands.
Fibers {massa intermedia} link left and right thalamus.
Peanut-sized thalamus nuclei {medial dorsal nucleus} can be for emotions and receive from and send to amygdala and prefrontal cortex, mostly orbitofrontal cortex. Intralaminar nuclei surround it.
Thalamus nuclei {medial geniculate nucleus} can be for sound; receive from cochlea, lateral lemniscus, and inferior colliculus; and send to temporal lobe.
Lateral thalamic nuclei {medial lateral thalamic nucleus} can be for memory.
Thalamic regions {medial lemniscus} can mix input from touch receptors, thermoreceptors, and nociceptors along spinothalamic tract. Descending inhibition enhances contrast between stimulated area and adjacent regions or admits only certain input to higher levels, and so affects attention.
Parvocellular cells receive from bipolar cells with small dendrite trees {midget cell} and send sustained signals to visual-cortex layer 4cbeta. Small cells are for color, spatial resolution, texture, shape, depth perception, and stereopsis [Merigan and Maunsell, 1993] [Schiller and Logothetis, 1990].
Thalamus regions {motor thalamus} can connect to basal ganglia, cerebellum, motor neocortex, vagus nerve, and hypothalamus and is in visceral and autonomic system.
Parvocellular cells {parvocellular layer} receive from midget bipolar cells with small dendrite trees and send sustained signals to visual-cortex layer 4cbeta. Small cells are for color, spatial resolution, texture, shape, depth perception, and stereopsis [Merigan and Maunsell, 1993] [Schiller and Logothetis, 1990].
Thalamus nuclei {pulvinar nucleus} can have inferior, lateral, and medial nuclei that are for attention, are multisensory, and receive from superior colliculus and retinal ganglion cells [Desimone et al., 1990] [Grieve et al., 2000] [Kinomura et al., 1996] [LaBerge and Buchsbaum, 1990] [LaBerge, 2000] [Rafal and Posner, 1987] [Robinson and Cowie, 1997] [Robinson and Petersen, 1992]. Pulvinar nucleus excites posterior parietal and inferior temporal lobes for external stimuli. Nucleus sides {lateral pulvinar nucleus} inhibit cerebral cortex to suppress irrelevant events, increase resolution, minimize receptive fields, and specify attention focus.
Thin cell sheet {reticular nucleus} {nucleus reticularis thalami} (nRt) surrounds thalamus and has only inhibitory GABA neurons. Reticular nucleus receives from most axons to and from neocortex and interacts with its own neurons. It sends output to thalamus, to organize sleep rhythms, such as deep-sleep spindling and delta waves, and select sense channels to cortex.
thalamus nucleus {semilunaris nucleus}.
Thalamus regions {sensory thalamus} can have reverberatory circuit from reticular formation and hypothalamus to cortex. It carries wakefulness impulses. It mediates contact, temperature, and pain consciousness. It has anterior, lateral geniculate, medial-lateral, pulvinar, semilunaris, and ventral centrum medianum nuclei.
Motor nucleus {ventral anterior thalamic nucleus} receives from cerebellum and globus pallidus and sends to corpus striatum.
thalamus nucleus {ventral centrum medianum nucleus}.
Motor nucleus {ventral lateral thalamic nucleus} receives from cerebellum and globus pallidus and sends to cerebral motor cortex.
Thalamic region {ventral medial basal thalamus} receives from parabrachial nucleus and nucleus tractus solitarius and sends to posterior insula.
Thalamic region {ventral medial posterior thalamus} receives from trigeminal nucleus and sends to posterior insula.
Thalamic region {ventral posterior thalamic nuclei} includes sensory ventral posterolateral nucleus and ventral posteromedial nucleus. It receives from medial lemniscus, spinothalamic tract, and trigeminal nerve and sends to postcentral gyrus.
Thalamus nucleus {ventrobasal complex} receives from dorsal column nuclei and sends to primary somatosensory cortex.
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