Michael Steven Anthony Graziano (born May 22, 1967 [1] ) is an American scientist and novelist who is currently a professor of Psychology and Neuroscience at Princeton University. [2] His scientific research focuses on the brain basis of awareness. He has proposed the "attention schema" theory, an explanation of how, and for what adaptive advantage, brains attribute the property of awareness to themselves. [3] [4] His previous work focused on how the cerebral cortex monitors the space around the body [5] [6] [7] [8] [9] [10] [11] and controls movement within that space. [12] [13] [14] [15] [16] [17] [18] [19] Notably he has suggested that the classical map of the body in motor cortex, the homunculus, is not correct and is better described as a map of complex actions that make up the behavioral repertoire. [20] His publications on this topic have had a widespread impact among neuroscientists but have also generated controversy. [21] [22] [23] His novels [24] [25] rely partly on his background in psychology and are known for surrealism or magic realism. [26] [27] [28] Graziano also composes music including symphonies [29] and string quartets. [30]
Graziano was born in Bridgeport Connecticut in 1967 and spent his childhood in Buffalo, New York. He received his Bachelor of Arts degree from Princeton University in 1989 in Psychology. He attended graduate school in neuroscience at MIT from 1989 to 1991 and then returned to Princeton University to complete his doctoral degree in 1996, in Neuroscience and Psychology. He remained at Princeton University as a postdoctoral researcher and then as a professor of neuroscience and psychology.
Graziano has made contributions in three areas of neuroscience: how neurons in the primate brain encode peripersonal space, how the motor cortex controls complex movement, and the possible neuronal basis of consciousness. These contributions are detailed in the following sections.
In the 1990s, Graziano with Charles Gross described the properties of a set of multisensory neurons in the monkey brain. Building on the work of Hyvarinen and colleagues [31] [32] and Rizzolatti and colleagues [33] [34] Graziano and Gross described a network of brain areas that appeared to encode the space immediately surrounding the body. [7] [8] [9] [10] [11]
Each multisensory neuron responded to a touch within a specific "tactile receptive field" on the body surface. Each neuron also responded to a visual stimulus near or approaching the tactile receptive field. The "visual receptive field" was therefore a region of nearby space affixed to the relevant body part. Some neurons responded to sound sources near the tactile receptive field. [7] Some neurons also responded mnemonically, becoming active when a part of the body moved through space and approached the remembered location of an object in the dark. [8] The activity of these multisensory neurons therefore signaled the presence of an object near or touching a part of the body, regardless of whether the object was felt, seen, heard, or remembered.
Electrical stimulation of these multisensory neurons almost always evoked a complex, coordinated movement that resembled a flinching, blocking, or protecting action. [16] [17] [18] [19] Chemical inhibition of these neurons produced a "nerves of steel" state in which defensive reactions were inhibited. [16] Chemical enhancement of these neurons produced a "super flincher" state in which any mild stimulus, such as an object gently moved toward the face, evoked a full-blown flinching reaction. [16]
In Graziano's interpretation, [35] these multisensory neurons form a specialized brain-wide network that encodes the space near the body, computes a margin of safety, and helps to coordinate movements in relation to nearby objects with an emphasis on withdrawal or blocking movements. A subtle level of activation might bias ongoing behavior to avoid collision, whereas a strong level of activation evidently causes an overt defensive action.
The neurons that encode peripersonal space may also provide a neuronal basis for the psychological phenomenon of personal space. [35] Personal space, described by Hall, [36] is the flexible bubble of space around each person that is protected from intrusion by other people.
The peripersonal neurons may also play a central role in the body schema [37] an internally computed model of the body first proposed to exist by Head and Holmes in 1911. [38]
In the 2000s Graziano's lab obtained evidence suggesting that the motor cortex might not contain a simple map of the body's muscles as in classical descriptions such as Penfield's description of a motor homunculus. [39] Instead, the motor cortex may contain a mapping of coordinated, behaviorally useful actions that make up a typical movement repertoire.
In their initial experiments, Graziano and colleagues used electrical microstimulation on the motor cortex of monkeys. [15] [19] Most previous protocols in the motor cortex used very brief stimulation, such as for a hundredth of a second. Graziano applied the stimulation for half a second each time, on a behaviorally relevant time scale, in order to match the typical duration of a monkey's reaching and grasping. The longer stimulation train in Graziano's experiments evoked complex movements that included many joints and that resembled movements from the animal's behavioral repertoire.
For example, stimulation of one site always caused the hand to close in a grip, the arm to bring the hand to the mouth, and the mouth to open. Stimulation of another site always caused the grip to open, the palm to face away from the body, and the arm to extend, as if the monkey were reaching to grasp an object. Other sites evoked other complex movements. The behavioral repertoire of the animal seemed to be rendered onto the cortical sheet.
This initial work became controversial because of the method of stimulation on a behavioral time scale. The method was not commonly used in the study of motor cortex [40] although it had been used in the study of other brain regions. [20] That controversy may have partially distracted from the other methods used to study the action map. [20] For example, computational models [12] show that when the complex movement repertoire of a monkey is arranged in a flattened map, with similar movements represented near each other, the map closely resembles the known arrangement of the monkey motor cortex.
In Graziano's proposal, many of the complexities of the motor cortex, such as its overlapping maps of the body and its multiple areas with somewhat different mixtures of properties, may be a result of representing the many parts of the movement repertoire each with its own specialized computational requirements. Graziano [20] suggests that the action-map view does not contradict the more traditional view of motor cortex as a set of fields with differing functions. Instead, the action map may help to explain why motor cortex is divided into functionally distinct fields and why the fields are arranged spatially as they are.
Other researchers have since found a similar, ethological organization to motor cortical regions in monkeys, prosimians, cats, and rats. [21] [22] [41] [42] [43] Notwithstanding, direct tests of the idea that the motor cortex contains a movement repertoire have not corroborated this hypothesis. [23] Varying the initial position of the forelimb does not change the muscle synergies evoked by microstimulation of a motor cortical point. Consequently, the evoked movements reach nearly the same final end point and posture, with variability. [23] However, the movement trajectories are quite different depending on the initial limb posture and the starting position of the paw. The evoked movement trajectory is most natural when the forelimb lays pendant ~ perpendicular to the ground (i.e., in equilibrium with the gravitational force). From other starting positions, the movements do not appear natural. The paths of the paw are curved with changes and reversals of direction and the passive influence of the gravitational force on the movements is obvious. These observations demonstrate that while the output of the cortical point evokes a seemingly coordinated limb movement from a rest position, it does not specify a particular movement direction or a controlled trajectory from other initial positions. Thus, in natural conditions a controlled movement must depend on the coordinated activation of a multitude of cortical points, terminating at a final locus of motor cortical activity, which holds the limb at a spatial location. [23]
Since 2010 Graziano's lab has studied the brain basis of consciousness. Graziano [44] [45] proposed that specialized machinery in the brain computes the feature of awareness and attributes it to other people in a social context. The same machinery, in that hypothesis, also attributes the feature of awareness to oneself. Damage to that machinery disrupts one's own awareness.
The attention schema theory (AST) seeks to explain how an information-processing machine could act the way people do, insisting it has consciousness, describing consciousness in the ways that we do, and claiming that it has an inner magic that transcends mere information-processing, even though it does not. AST is currently being incorporated into artificial intelligence systems through the work of the international Astound project.
The proposed AST was partly motivated by two sets of previous findings.
First, certain regions of the cortex are recruited during social perception as people construct models of other people's minds. [46] [47] [48] [49] [50] [51] [52] [53] These regions include, among other areas, the superior temporal sulcus (STS) and the temporoparietal junction (TPJ) bilaterally but with a strong emphasis on the right hemisphere.
Second, when these same regions of cortex are damaged, people suffer from a catastrophic disruption of their own awareness of events and objects around them. The clinical syndrome of hemispatial neglect, or loss of awareness of one side of space, is particularly profound after damage to the TPJ or STS in the right hemisphere. [54] [55]
The conjunction of these two previous findings led to the suggestion that awareness may be a computed feature constructed by an expert system in the brain, that at least partly overlaps the TPJ and STS. In that proposal, the feature of awareness can be attributed to other people in the context of social perception. It can also be attributed to oneself, in effect creating one's own awareness.
Why construct the feature of awareness and attribute it to other people? In order to understand and predict the behavior of other people, it is useful to monitor other people's attentional state. Attention is a data handling method by which some signals in the brain are enhanced at the expense of others. According to the AST, [45] when the brain computes that person X is aware of thing Y, it is in effect modeling the state in which person X is applying an attentional enhancement to signal Y. Awareness is an attention schema. In that theory, the same process can be applied to oneself. One's own awareness is a schematized model of one's own attention.
Graziano writes literary novels under his own name and children's novels under the pseudonym B. B. Wurge. His stated reason for the pseudonym is to ensure that children do not accidentally read the wrong category of book. [56] His novels have been praised for their originality, vividness, and surreal imagination. [26] [27] [28] His book for children, The Last Notebook of Leonardo, won the 2011 Moonbeam Award.
His books include:
Literary Novels:
Children's Novels (written under the name B. B. Wurge):
Books on Neuroscience:
Books of music:
The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus.
The claustrum is a thin sheet of neurons and supporting glial cells, that connects to the cerebral cortex and subcortical regions including the amygdala, hippocampus and thalamus of the brain. It is located between the insular cortex laterally and the putamen medially, encased by the extreme and external capsules respectively. Blood to the claustrum is supplied by the middle cerebral artery. It is considered to be the most densely connected structure in the brain, and thus hypothesized to allow for the integration of various cortical inputs such as vision, sound and touch, into one experience. Other hypotheses suggest that the claustrum plays a role in salience processing, to direct attention towards the most behaviorally relevant stimuli amongst the background noise. The claustrum is difficult to study given the limited number of individuals with claustral lesions and the poor resolution of neuroimaging.
In neuroanatomy, the superior colliculus is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates, the homologous structure is known as the optic tectum or optic lobe. The adjective form tectal is commonly used for both structures.
A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another. Thus, the neuron "mirrors" the behavior of the other, as though the observer were itself acting. Mirror neurons are not always physiologically distinct from other types of neurons in the brain; their main differentiating factor is their response patterns. By this definition, such neurons have been directly observed in humans and primate species, and in birds.
The motor cortex is the region of the cerebral cortex involved in the planning, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately anterior to the central sulcus.
A gamma wave or gamma rhythm is a pattern of neural oscillation in humans with a frequency between 25 and 140 Hz, the 40 Hz point being of particular interest. Gamma rhythms are correlated with large-scale brain network activity and cognitive phenomena such as working memory, attention, and perceptual grouping, and can be increased in amplitude via meditation or neurostimulation. Altered gamma activity has been observed in many mood and cognitive disorders such as Alzheimer's disease, epilepsy, and schizophrenia.
A neuronal ensemble is a population of nervous system cells involved in a particular neural computation.
The premotor cortex is an area of the motor cortex lying within the frontal lobe of the brain just anterior to the primary motor cortex. It occupies part of Brodmann's area 6. It has been studied mainly in primates, including monkeys and humans. The functions of the premotor cortex are diverse and not fully understood. It projects directly to the spinal cord and therefore may play a role in the direct control of behavior, with a relative emphasis on the trunk muscles of the body. It may also play a role in planning movement, in the spatial guidance of movement, in the sensory guidance of movement, in understanding the actions of others, and in using abstract rules to perform specific tasks. Different subregions of the premotor cortex have different properties and presumably emphasize different functions. Nerve signals generated in the premotor cortex cause much more complex patterns of movement than the discrete patterns generated in the primary motor cortex.
The supplementary motor area (SMA) is a part of the motor cortex of primates that contributes to the control of movement. It is located on the midline surface of the hemisphere just in front of the primary motor cortex leg representation. In monkeys the SMA contains a rough map of the body. In humans the body map is not apparent. Neurons in the SMA project directly to the spinal cord and may play a role in the direct control of movement. Possible functions attributed to the SMA include the postural stabilization of the body, the coordination of both sides of the body such as during bimanual action, the control of movements that are internally generated rather than triggered by sensory events, and the control of sequences of movements. All of these proposed functions remain hypotheses. The precise role or roles of the SMA is not yet known.
Premovement neuronal activity in neurophysiological literature refers to neuronal modulations that alter the rate at which neurons fire before a subject produces movement. Through experimentation with multiple animals, predominantly monkeys, it has been shown that several regions of the brain are particularly active and involved in initiation and preparation of movement. Two specific membrane potentials, the bereitschaftspotential, or the BP, and contingent negative variation, or the CNV, play a pivotal role in premovement neuronal activity. Both have been shown to be directly involved in planning and initiating movement. Multiple factors are involved with premovement neuronal activity including motor preparation, inhibition of motor response, programming of the target of movement, closed-looped and open-looped tasks, instructed delay periods, short-lead and long-lead changes, and mirror motor neurons.
In cognitive neuroscience, visual modularity is an organizational concept concerning how vision works. The way in which the primate visual system operates is currently under intense scientific scrutiny. One dominant thesis is that different properties of the visual world require different computational solutions which are implemented in anatomically/functionally distinct regions that operate independently – that is, in a modular fashion.
The posterior parietal cortex plays an important role in planned movements, spatial reasoning, and attention.
Body schema is an organism's internal model of its own body, including the position of its limbs. The neurologist Sir Henry Head originally defined it as a postural model of the body that actively organizes and modifies 'the impressions produced by incoming sensory impulses in such a way that the final sensation of body position, or of locality, rises into consciousness charged with a relation to something that has happened before'. As a postural model that keeps track of limb position, it plays an important role in control of action.
Microstimulation is a technique that stimulates a small population of neurons by passing a small electrical current through a nearby microelectrode.
The neural correlates of consciousness (NCC) are the minimal set of neuronal events and mechanisms sufficient for the occurrence of the mental states to which they are related. Neuroscientists use empirical approaches to discover neural correlates of subjective phenomena; that is, neural changes which necessarily and regularly correlate with a specific experience. The set should be minimal because, under the materialist assumption that the brain is sufficient to give rise to any given conscious experience, the question is which of its components are necessary to produce it.
Electrical brain stimulation (EBS), also referred to as focal brain stimulation (FBS), is a form of electrotherapy used as a technique in research and clinical neurobiology to stimulate a neuron or neural network in the brain through the direct or indirect excitation of its cell membrane by using an electric current. EBS is used for research or for therapeutic purposes.
Vittorio Gallese is professor of Psychobiology at the University of Parma, Italy, and was professor in Experimental Aesthetics at the University of London, UK (2016–2018). He is an expert in neurophysiology, cognitive neuroscience, social neuroscience, and philosophy of mind. Gallese is one of the discoverers of mirror neurons. His research attempts to elucidate the functional organization of brain mechanisms underlying social cognition, including action understanding, empathy, language, mindreading and aesthetic experience.
The primary motor cortex is a brain region that in humans is located in the dorsal portion of the frontal lobe. It is the primary region of the motor system and works in association with other motor areas including premotor cortex, the supplementary motor area, posterior parietal cortex, and several subcortical brain regions, to plan and execute voluntary movements. Primary motor cortex is defined anatomically as the region of cortex that contains large neurons known as Betz cells, which, along with other cortical neurons, send long axons down the spinal cord to synapse onto the interneuron circuitry of the spinal cord and also directly onto the alpha motor neurons in the spinal cord which connect to the muscles.
Social cognitive neuroscience is the scientific study of the biological processes underpinning social cognition. Specifically, it uses the tools of neuroscience to study "the mental mechanisms that create, frame, regulate, and respond to our experience of the social world". Social cognitive neuroscience uses the epistemological foundations of cognitive neuroscience, and is closely related to social neuroscience. Social cognitive neuroscience employs human neuroimaging, typically using functional magnetic resonance imaging (fMRI). Human brain stimulation techniques such as transcranial magnetic stimulation and transcranial direct-current stimulation are also used. In nonhuman animals, direct electrophysiological recordings and electrical stimulation of single cells and neuronal populations are utilized for investigating lower-level social cognitive processes.
Eberhard Erich Fetz is an American neuroscientist, academic and researcher. He is a Professor of Physiology and Biophysics and DXARTS at the University of Washington.
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