Midbrain ganglia {cuneate nuclei} can receive texture, form, and vibration information in medulla ipsilateral cuneate tracts and send to thalamus, cerebrum, and cerebellum. Maps are smaller than in other areas.
Midbrain nuclei {gracile nuclei} can receive texture, form, and vibration information in medulla ipsilateral gracile tracts and send to thalamus, cerebrum, and cerebellum. Maps are smaller than in other areas.
Midbrain nuclei {inferior colliculi} can send to superior colliculi. They have auditory functions and control eye movements.
Brainstem regions {inferior olive} (IO) can send to cerebellar Purkinje cells.
Midbrain striatum nucleus {nucleus accumbens} receives excitatory dopaminergic pathway from frontal lobes and ventral tegmentum and receives from basal and lateral amygdala. It sends to ventral pallidum. Nucleus accumbens mediates emotions and movements. Benzodiazepine anti-anxiety agent and antipsychotic agents block dopaminergic pathway activation. Regular drug use and other reward stimuli increase delta FosB transcription factor, which causes sensitization and degrades slowly, in nucleus accumbens.
Vertebrates other than mammals have vision cell layer {optic tectum} over large ventricle. Mammals have superior colliculi instead. In amphibia and fish, fibers from retina to tectum keep growing and changing. Mostly unimodal sense pathways go from cerebral cortex to tectum. Tectum makes eye saccades to focus attention-getting object on fovea. Divergence in individual tectum-nuclei loops explains how large recruited tectum-neuron population can form composite command observed at tectum.
Posterior upper brainstem region {parabrachial nuclei} (PBN) receives from sensory trigeminal nucleus and nucleus tractus solitarius and sends motor input to superior colliculi and motor output to hypothalamus and ventral medial basal thalamus.
Pons and thalamus nucleus {periaqueductal gray} (PAG) has opiate receptors and makes endorphins.
Brainstem nucleus {periolivary nucleus} near olive sends to superior colliculi.
Brainstem regions {posterior upper brainstem} can contain periaqueductal gray, parabrachial nucleus, monoamine nuclei, and acetylcholine nuclei. Damage to posterior upper brainstem causes coma.
Brainstem regions {quadrigeminal plate} can have superior and inferior colliculi.
Brainstem nucleus {red nucleus} {ruber nucleus} receives from amygdala and sends to hypothalamus paraventricular nucleus {stria terminalis}. It works similarly to motor cortex.
Brainstem regions {substantia nigra} {substantia nigra pars reticulata} can send to superior colliculus to control eye movement. Substantia nigra cholinergic neurons connect to sense and motor neurons in caudate nucleus and putamen in basal ganglia. Basal ganglia and other midbrain dopamine neurons inhibit caudate nucleus, corpus striatum, and thalamus to coordinate motor function and automatic movement. Alzheimer's disease degenerates substantia nigra neurons.
Mammal midbrain dorsal surface has large symmetrical bumps {superior colliculi} that mediate light accommodation, eyeball movements, body movements for vision, orientation, and attention [Aldrich et al., 1987] [Brindley et al., 1969] [Celesia et al., 1991].
anatomy
Superior colliculus has seven alternating cellular and fibrous layers with few interneurons, eight types of synaptic terminals, and broad dendrite arbors. Superficial layers I to III and deep layers IV to VII have topographic motor maps and associated visual and touch maps.
Superior colliculus removal causes failure to detect contralateral visual stimuli.
anatomy: input
Superior colliculus efferent neurons for eye movements receive input from substantia nigra.
Superior colliculus deep layers receive vision information ipsilaterally from lateral suprasylvian visual area and anterior ectosylvian visual area, not from striate visual cortex.
Deep layers receive somatosensory input from anterior ectosylvian sulcus dorsal part, contralateral sensory trigeminal complex, dorsal column nuclei, lateral cervical nucleus, and spinal cord. Contralateral sensory trigeminal complex receives C fibers and A-delta fibers.
Deep layers receive auditory input from anterior ectosylvian sulcus Field AES region, inferior colliculus contralateral brachium, inferior colliculus external nucleus, nucleus sagulum, and dorsomedial periolivary nucleus.
Deep layers receive motor input from frontal eye fields, motor cortex, zona incerta, thalamus reticular nucleus, posterior commissure nucleus, perihypoglossal nucleus, contralateral superior colliculus, locus coeruleus, raphé dorsalis, parabrachial nuclei, reticular formation, and hypothalamus.
Deep layers receive from basal ganglia through substantia nigra pars reticulata. Deep layers receive from cerebellum deep nuclei, including medial and posterior interposed nuclei.
anatomy: output
Superior colliculus deep layers send to thalamus, opposite superior colliculus, brainstem, and spinal cord. Superior colliculus deep layers connect to sense and motor cerebral cortex and to brainstem and spinal cord, to position peripheral sense organs. Deep layers also send contralaterally to tegmentum and spinal cord to reposition eyes, head, limbs, ears, and whiskers.
neurons: receptive field
Superior-colliculus neurons have central ON zones surrounded by lower sensitivity areas, not like retina and lateral-geniculate-nucleus ON-center-neuron or OFF-center-neuron receptive fields. Receptive fields are larger than in lateral geniculate or cortex neurons. Border is inhibitory {suppressive zone}. The most-effective stimulus is smaller than receptive field. Moving or flashing stimuli are more effective than stationary ones. Movement direction is more effective. Slow movements are more effective than rapid ones. Repeating same stimulus produces response habituation.
neurons: noxious
Superior colliculus neurons {nociceptive-specific neuron} (NS) can respond to noxious stimuli. Superior colliculus neurons {wide dynamic range neuron} (WDR) can respond to all mechanical stimuli, but especially to noxious mechanical or thermal stimuli.
neurons: multisensory
Superior colliculus neurons are 25% unimodal and 75% multisensory. Multisensory and unimodal neurons typically require 100 milliseconds to process information, but some multisensory neurons take 1500 milliseconds.
neurons: auditory
Superior colliculus has four auditory neuron types. Compared to cortical auditory neurons, superior colliculus auditory neurons are more insensitive to pure tones and more sensitive to spatial location, interaural time, and intensity differences. They respond better to moving stimuli, have directional selectivity, habituate to repeated stimuli, and have restricted receptive fields with maximal-response regions.
neurons: somatosensory
Superior colliculus somatosensory neurons respond to hair or skin stimulation, have well-defined receptive fields, prefer intermediate-velocity or high-velocity stimuli, habituate rapidly, are large, have best regions, have no inhibitory surrounding areas, and have no directional selectivity.
neurons: movement field
Midbrain neuron receptive fields {movement field} are like sense-neuron receptive fields. Neurons with similar movement fields are in same superior colliculus region. If neuron activity exceeds threshold, amount above threshold determines saccade movement velocity and distance.
eye movement
Mammal superior colliculi and non-mammal optic tectum process multisensory information, shift attention, and control voluntary and involuntary eye and other sense-organ movements, for orientation and attention. Stimulation shifts eyes, ears, and head to focus on stimulus location. High intensity causes withdrawal or escape.
Anteromedial superior colliculi stimulation causes contralateral, upward, and parallel conjugate eye movement.
Lateral superior colliculi stimulation causes conjugate, contralateral, and downward movement.
To initiate eye movement to periphery, caudal superior colliculus, which represents peripheral visual space, has pre-motor activity.
Visual fixation involves neurons in rostral superior colliculus.
eye movement: saccade
Superior colliculus neurons {motor error neuron} can generate low-frequency, long-duration discharge to signal difference between current eye position and target position. Superior colliculus neurons can initiate saccades and determine speed, direction, and amplitude [Corbetta, 1998] [Schall, 1991] [Schiller and Chou, 1998]. Saccade initiation and velocity, duration, and direction specification are separate processes. Saccade commands are many-neuron vector sums.
Brainstem regions {superior olive} can measure time and intensity differences to differentiate auditory-signal arrival times. Olive sides {lateral superior olive} (LSO) receive inputs from both ears for intensity-level-difference detection. Olive middle {medial superior olive} (MSO) receives inputs from both ears, for time-difference detection. Neurons have time-difference ranges.
Brainstem region {ventral tegmentum} {ventral tegmental area} (VTA) is for pleasure and motivation. Dopamine neurons inhibit nucleus accumbens, mesolimbic system, frontal cortex, and sensorimotor cortex.
4-Zoology-Organ-Nerve-Brain-Brainstem
Outline of Knowledge Database Home Page
Description of Outline of Knowledge Database
Date Modified: 2022.0225