Anterior cingulate gyrus, cortex, and basal ganglia make circuit {anterior attention network} that detects expected location. Cortex notes matches, and basal ganglia note mismatches.
Dorsolateral prefrontal cortex, cingulate nucleus, frontal eye fields in area 8, posterior parietal lobe in area 7a, pulvinar nucleus, and superior colliculus change object attention {attention shift} [Astafiev et al., 2003] [Corbetta, 1998] [Kustov and Robinson, 1996] [Mountcastle et al., 1981] [Sheliga et al., 1994] [Shepherd et al., 1986] [Wurtz et al., 1982].
The largest descending fiber tract {corticospinal motor tract} has one million axons from primary motor, supplementary motor, and premotor cerebral cortex layer-5 pyramidal neurons to spinal cord segment neurons to control precise finger and toe movements. Spinal-cord axons initiate skilled muscle movements at alpha motor neurons. Pre-central gyrus has the most corticospinal motor-tract neurons.
Lateral corticospinal tract, only in mammals, controls voluntary muscles. Anterior corticospinal tract does not cross over and is for posture and trunk position.
Signals from skin, muscles, tendons, and joints travel in spinal-cord dorsal column large and fast fibers to gracile nucleus and cuneate nucleus, then to thalamus medial lemniscus, then to post-central gyrus {dorsal-column-medial-lemniscal pathway} {DCML pathway}, which is for reflexes and rapid movement.
Axons from retina nasal halves, after traveling in optic nerve, cross over {decussation, axon} to other side in brain front middle optic chiasma.
Tracts {extrapyramidal tract} can include caudate nucleus, globus pallidus, putamen, red nucleus, reticular formation, and substantia nigra unmyelinated axons.
Between thalamic and cortical regions, one connection is feedforward {feedforward circuit}, and the other is feedback {feedback circuit}. Connections never combine both.
feedforward
Feedforward axons begin in layers 2 and 3 and end in layer 4.
feedback
Feedback axons begin in layers 5 and 6 and end in layers 1, 2, 3, and 6. Feedback goes to larger regions than feedforward [Barone et al., 2000] [Bullier, 2001] [Bourassa and Deschenes, 1995] [Cauller and Kulics, 1991] [DiLollo et al., 2000] [Grossberg, 1999] [Grossenbacher, 2001] [Heimer, 1971] [Hupe et al., 1998] [Johnson and Burkhalter, 1997] [Lamme and Roelfsema, 2000] [Lamme and Spekreijse, 2000] [Kosslyn, 1980] [Kosslyn, 1994] [Kosslyn, 2001] [Ojima, 1994] [Pollen, 1995] [Pollen, 1999] [Pollen, 2003] [Rhodes and Llinás, 2001] [Rockland et al., 1997] [Rockland, 1994] [Rockland, 1996] [Rockland, 1997] [Rockland and Van Hoesen, 1994] [Salin and Bullier, 1995] [Supèr et al., 2001] [Wiener, 1947] [Williams and Stuart, 2002] [Williams and Stuart, 2003].
Networks {frontal lobe attentional network} can be for attention, executive functions, decision making, voluntary movements, and stimulus conflict resolution [Mountcastle et al., 1981] [Wurtz et al., 1982].
Cerebrum, basal ganglia, brainstem, and cerebellum send to motor-neuron reciprocal-inhibition neurons {internuncial neuron}.
Systems {interoceptive system} can control homeostasis and chemical changes. Hypothalamus can sense molecules that can cross blood-brain barrier. Circumventricular organs, brainstem area postrema, and cerebrum subfornical organs lack blood-brain barrier and can sense large molecules.
Networks {limb premotor recurrent network} can spread positive feedback for limb command generation. Purkinje-cell bands converge on small nuclear-cell clusters in topographically organized recurrent circuits, with thalamic, motor cortical, rubral, pontine, and lateral-reticular neurons, which send commands to spinal cord along corticospinal and rubrospinal fibers.
A pain-sensing system {nociceptive system} {nociceptive pain response} can use superior colliculus, spinal cord, and thalamus neurons. It has opiate receptors, so opiates can inhibit it. Tactile, nociceptive, and thermal receptor systems interact.
Axons from each-retina nasal half, after traveling in optic nerve, cross over {decussation, optic nerve} to other side in brain front middle {optic chiasma}. Temporal-lobe half-retina axons, after traveling in optic nerve, remain on same side at optic chiasma, so visual-field right half goes to right lateral geniculate body and cerebrum, and left half goes to left.
Brain networks {premotor network} can control eye movements using recurrent pathways.
functions Separate premotor networks control smooth and saccadic eye movements. Separate premotor networks control horizontal and vertical movements.
input
Premotor network receives vestibular-sense input from semicircular canals. Vestibular nucleus signals use velocity coding. On brainstem sides, medial-vestibular-nucleus neurons interconnect with prepositus-hypoglossius neurons and with intermediate types. Prepositus hypoglossius neuron signals use position coding. Brainstem sides interconnect through recurrent inhibitory pathway.
Mammalian tracts {pyramidal tract} can excite motor neurons and enhance reflexes. Muscle actions, but not skilled-movement learning or memory, require pyramidal tract, which is bigger if cortex is bigger.
Septum and hippocampus circuit {septo-hippocampal system} affects contextual and spatial memory.
Perirhinal cortex receives multisensory input and sends to hippocampus, which sends to diencephalon {short-term memory circuit} to make short-term memory [Aksay et al., 2001] [Compte et al., 2000] [Courtney et al., 1998] [de Fockert et al., 2001] [Eichenbaum, 2002] [Fuster, 1973] [Fuster, 1995] [Fuster, 1997] [Gazzaniga, 2000] [Goldman-Rakic, 1992] [Goldman-Rakic, 1995] [Goldman-Rakic et al., 2000] [Miller, 1999] [Miller et al., 1996] [Pochon et al., 2001] [Rao et al., 1997] [Romo et al., 1999] [Squire and Kandel, 1999] [Squire, 1992].
Vibration, steady pressure, and light touch information goes from skin, to spinal-cord dorsal root, to brainstem lower end, to thalamus ventro-basal complex, and to primary somatosensory cerebral cortex {skin sensory circuit}. All senses have similar circuits.
Body systems {somatosensory system} can have viscera, vestibular, proprioception, and kinesthesia systems and autonomic, homeostasis, and fine touch functions. Somatosensory system uses reticulum, monoamine nuclei, acetylcholine nuclei, hypothalamus, basal forebrain, insular cortex, S2 cortex, and medial parietal cortex.
Body systems {spatial attention system} can regulate inferotemporal neurons and filter inferotemporal-area input from selected stimulus and memory, for pattern recognition.
Proprioception input goes to nucleus dorsalis, then to ipsilateral dorsal spinocerebellar tract or to contralateral ventral spinocerebellar tract, then to cerebellum, and then to cerebral cortex {spinocerebellar tract}. Dorsal and ventral spinocerebellar tracts are for movement initiation or for position information from muscle spindles, Golgi tendon organs, and touch receptors.
Tracts {spinoreticular tract} can be for dull and chronic pain from soma.
Diffuse touch, pressure, acute pain, and thermal fibers {spinothalamic pathway} {spinothalamic tract} {protopathic pathway} {spinothalamic system} go to substantia gelatinosa as unmyelinated fibers, cross to contralateral spinothalamic tracts, go through reticular system, go to thalamus ventral posterior nucleus, and end at cerebrum. Spinothalamic tract has small and slow feedback nerves for pain inhibition.
Older unconscious visual pathway {tectopulvinar pathway} {tectofugal pathway} goes from tectum to superior colliculus, thalamus pulvinar nucleus, and parietal lobe and is for visual spatial orientation, orienting responses, and movement to focus attention. Geniculostriate and tectopulvinar pathways interact [Ramachandran, 2004].
Spinal-cord tracts {tectospinal tract} can be for reflex head turns.
Pathways {vestibulo-ocular pathway} from retina to vestibular system to cerebellum can allow eye to track moving objects smoothly while head turns.
Spinal-cord tracts {vestibulospinal tract} can be for posture reflexes.
Circuits {dorsal system} {dorsal pathway} {vision-for-action} {where pathway} {how pathway} {high path for vision} {ambient system} can go from occipital lobe area V1 to mediotemporal (MT) area, parietal area PG, posterior parietal area (PPC), and dorsolateral prefrontal cortex [Bridgeman et al., 1979] [Rossetti, 1998] [Ungerleider and Mishkin, 1982] [Yabuta et al., 2001] [Yamagishi et al., 2001].
functions
Dorsal pathway processes object location, size, parts, and characteristics. It converts spatial properties from retinotopic coordinates to spatiotopic coordinates. It tracks unconscious motor activity and guides conscious actions, such as reaching and moving eyes.
output
Dorsal system sends to amygdala and hippocampus to form visual memories [Heimer, 1971].
Circuits {ventral system} {vision-for-perception} {what pathway} {low path for vision} {focal system} can go from occipital-lobe area V1, through areas V2 and V3 and V4, to inferior temporal lobe area TE, limbic system, and ventrolateral prefrontal lobe [Bridgeman et al., 1979] [Epstein and Kanwisher, 1998] [Haxby et al., 2001] [Heimer, 1971] [Ishai et al., 2000] [Milner and Goodale, 1995] [Ungerleider and Mishkin, 1982].
functions
Ventral system is for recognition. It classifies stimuli shapes and qualities. It registers new category instances. It responds to patterns, shapes, colors, and textures, with earlier neurons for smaller and later neurons for bigger. It does not contain representations but organizes input into familiar packets.
output
Ventral system sends to amygdala and hippocampus to form visual memories.
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Date Modified: 2022.0225