Michael Graziano

The peripersonal neurons may also play a central role in the body schema an internally computed model of the body first proposed to exist by Head and Holmes in 1911.

Michael Steven Anthony Graziano (born May 22, 1967 ) is an American scientist and novelist who is currently a professor of Psychology and Neuroscience at Princeton University.

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.

His previous work focused on how the cerebral cortex monitors the space around the body and controls movement within that space.

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.

His publications on this topic have had a widespread impact among neuroscientists but have also generated controversy.

His novels rely partly on his background in psychology and are known for surrealism or magic realism.

Graziano also composes music including symphonies and string quartets.

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 and Rizzolatti and colleagues Graziano and Gross described a network of brain areas that appeared to encode the space immediately surrounding the body.

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.

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.

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.

Chemical inhibition of these neurons produced a "nerves of steel" state in which defensive reactions were inhibited.

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.

In Graziano's interpretation, 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.

Personal space, described by Hall, is the flexible bubble of space around each person that is protected from intrusion by other people.

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.

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.

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.