The lateral postcentral gyrus is bounded by: 1) medial longitudinal fissure medially (to the middle)  2) central sulcus rostrally (in front)  3) postcentral sulcus caudally (in back)  4) lateral sulcus inferiorly (underneath)

It is the location of primary somatosensory cortex, the main sensory receptive area for the sense of touch. Like other sensory areas, there is a map of sensory space called a homunculus in this location. For the primary somatosensory cortex, this is called the sensory homunculus.

 

 

 

ScienceNews.org, July19, 2011, by Laura Sanders  —  When a woman born without limbs watches someone else sew, copycat regions in her brain activate even though she can’t hold a needle herself. Additional brain regions also lend support, demonstrating how flexible the brain is when it comes to observing and understanding the actions of others.

Scientists have known for over a decade about the mirror system, a network of brain regions usually activated by watching and performing an action. But just how the brain smoothly and quickly intuits what other people are doing, particularly when the action isn’t something the observer can do, has been unclear, says study coauthor Lisa Aziz-Zadeh of the University of Southern California in Los Angeles.

In the study, a middle-aged, healthy woman born with no arms and legs underwent brain scans as she watched videos of people performing actions such as holding and eating an apple slice, sewing with a needle and tapping a finger. Actions that the woman was capable of performing herself activated the mirror system, including parts of the brain that control movement. Mirror areas kicked in even for tasks the woman accomplishes in a different way, such as picking up food using her mouth instead of hands. (The participant had prosthetics briefly as a teenager but hadn’t used them in the past 40 years.)

When the woman witnessed actions that were impossible for her, such as using scissors, her brain’s mirror system still kicked in, but additional brain regions were recruited to help. These extra regions aren’t normally needed when people watch a task they’re able to perform, the researchers write in an upcoming Cerebral Cortex. These regions are thought to be involved in a process called “mentalizing,” in which a person tries to understand what someone else is thinking.

“What’s interesting is that even when she can’t do it, when it’s impossible for her, she still recruits her mirror system, but she additionally recruits these mentalizing regions,” Aziz-Zadeh says.

By suggesting that the mentalizing system kicks in for this woman when she cannot copy an action, the new study helps clarify how these two brain systems work together, says cognitive neuroscientist Marcel Brass of Ghent University in Belgium.

 

The same part of the brain activates whether performing or observing an action. Activity increases (red in brain model) when the context of an observed action reveals intention. (Credit: Marco Iacoboni/Ahmanson-Lovelace Brain Mapping Center at UCLA)

 

 

 

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 behaviour of the other, as though the observer were itself acting. Such neurons have been directly observed in primate and other species including birds. In humans, brain activity consistent with that of mirror neurons has been found in the premotor cortex, the supplementary motor area, the primary somatosensory cortex and the inferior parietal cortex.

Mirror neurons were first described in 1992. Some scientists consider this to be one of the most important recent discoveries in neuroscience. Among them is V.S. Ramachandran, who believes they might be very important in imitation and language acquisition. However, despite the excitement generated by these findings, to date no widely accepted neural or computational models have been put forward to describe how mirror neuron activity supports cognitive functions such as imitation.

The function of the mirror system is a subject of much speculation. Many researchers in cognitive neuroscience and cognitive psychology consider that this system provides the physiological mechanism for the perception action coupling (see the common coding theory). These mirror neurons may be important for understanding the actions of other people, and for learning new skills by imitation. Some researchers also speculate that mirror systems may simulate observed actions, and thus contribute to theory of mind skills, while others relate mirror neurons to language abilities. It has also been proposed that problems with the mirror system may underlie cognitive disorders, particularly autism. However the connection between mirror neuron dysfunction and autism is tentative and it remains to be seen how mirror neurons may be related to many of the important characteristics of autism.

The issue of gender differences in empathy is quite controversial and subject to social desirability and stereotypes. However, a series of recent studies conducted by Yawei Cheng, using a variety of neurophysiological measures, including MEG, spinal reflex excitability,[ electroencephalography, have documented the presence of a gender difference in the human mirror neuron system, with female participants exhibiting stronger motor resonance than male participants.

 

 

Diagram of the brain, showing the locations of the frontal and parietal lobes of the cerebrum, viewed from the left. The inferior frontal lobe is the lower part of the blue area, and the superior parietal lobe is the upper part of the yellow area.

 

 

 

It is not normally possible to study single neurons in the human brain, so most evidence for mirror neurons in humans is indirect. Brain imaging experiments using functional magnetic resonance imaging (fMRI) have shown that the human inferior frontal cortex and superior parietal lobe is active when the person performs an action and also when the person sees another individual performing an action. It has been suggested that these brain regions contain mirror neurons, and they have been defined as the human mirror neuron system.  ]More recent experiments have shown that even at the level of single participants, scanned using fMRI, large areas containing multiple fMRI voxels increase their activity both during the observation and execution of actions.

 

Neuropsychological studies looking at lesion areas that cause action knowledge, pantomime interpretation, and biological motion perception deficits have pointed to a causal link between the integrity of the inferior frontal gyrus and these behaviours. Transcranial magnetic stimulation studies have confirmed this as well.  These results indicate the activation in mirror neuron related areas are unlikely to be just epiphenomenal.

A study published in April 2010 reports recordings from single neurons with mirror properties in the human brain.  Mukamel et al (Current Biology, 2010) recorded from the brains of 21 patients who were being treated at Ronald Reagan UCLA Medical Center for intractable epilepsy. The patients had been implanted with intracranial depth electrodes to identify seizure foci for potential surgical treatment. Electrode location was based solely on clinical criteria; the researchers, with the patients’ consent, used the same electrodes to “piggyback” their research. The experiment included three parts: facial expressions, grasping and a control experiment. Activity from a total of 1,177 neurons in the 21 patients was recorded as the patients both observed and performed grasping actions and facial gestures. In the observation phase, the patients observed various actions presented on a laptop computer. In the activity phase, the subjects were asked to perform an action based on a visually presented word. In the control task, the same words were presented and the patients were instructed not to execute the action. The researchers found a small number of neurons that fired or showed their greatest activity both when the individual performed a task and when they observed a task. Other neurons had anti-mirror properties, that is, they responded when the participant saw an action but were inhibited when the participant performed that action. The mirror neurons found were located in the supplementary motor area and medial temporal cortex (other brain regions were not sampled). For purely practical reasons, these regions are not the same as those in which mirror neurons had been recorded from in the monkey: researchers in Parma were studying the ventral premotor cortex and the associated inferior parietal lobe, two regions in which epilepsy rarely occurs, and hence, single cell recordings in these regions are not usually done in humans. On the other hand, no one has to date looked for mirror neurons in the supplementary motor area or the medial temporal lobe in the monkey. Together, this therefore does not suggest that humans and monkeys have mirror neurons in different locations, but rather than they may have mirror neurons both in the ventral premotor cortex and inferior parietal lobe, where they have been recorded in the monkey, and in the supplementary motor areas and medial temporal lobe, where they have been recorded from in human – especially because detailed human fMRI analyses suggest activity compatible with the presence of mirror neurons in all these regions.

 

The parietal lobe is a part of the Brain positioned above (superior to) the occipital lobe and behind (posterior to) the frontal lobe. The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the dorsal stream of the visual system. This enables regions of the parietal cortex to map objects perceived visually into body coordinate positions. The name derives from the overlying parietal bone, which is named from the Latin pariet-, wall.

 

 

 

Mirror Neuron System in Autism: Broken or Just Slowly Developing?

 

This graph shows the relationship between age and mirror activity for a normal brain and one with autism. Source: ScienceDaily.com

 

 

 

ScienceDaily.com, Spring/Summer 2011   —   Developmental abnormalities in the mirror neuron system may contribute to social deficits in autism.

The mirror neuron system is a brain circuit that enables us to better understand and anticipate the actions of others. These circuits activate in similar ways when we perform actions or watch other people perform the same actions.

Now, a new study published in Biological Psychiatry reports that the mirror system in individuals with autism is not actually broken, but simply delayed.

Dr. Christian Keysers, lead author on the project, detailed their findings, “While most of us have their strongest mirror activity while they are young, autistic individuals seem to have a weak mirror system in their youth, but their mirror activity increases with age, is normal by about age 30 and unusually high thereafter.”

This increase in function of mirror neuron systems may be related to increased capacity for social function or responsiveness to rehabilitative treatments among individuals with autism.

“The finding of late developing circuit functions could be very important. One wonders whether the recent breakthroughs in the genetics of autism could help to identify causes for the developmental delays. This type of bridge might help to identify novel treatment mechanisms for autism,” said Dr. John Krystal, Editor of Biological Psychiatry.

One of the next steps in this line of research will be for researchers to examine how individuals with autism accomplish this improvement over time, and how therapeutic interventions targeting the same mechanism can help to support this important process.


Journal Reference:

  1. 1.                     Jojanneke A. Bastiaansen, Marc Thioux, Luca Nanetti, Christiaan van der Gaag, Cees Ketelaars, Ruud Minderaa, Christian Keysers. Age-Related Increase in Inferior Frontal Gyrus Activity and Social Functioning in Autism Spectrum Disorder. Biological Psychiatry, 2011; 69 (9): 832 DOI: 10.1016/j.biopsych.2010.11.007

 

 

 

Mirror Neurons, Self-Understanding And Autism Research

 

Research suggests that mirror neuron activity is fully developed by age 7. Scientists note that reading people’s expressions and interpreting their intentions may draw from similar activity in the brain. (Credit: iStockphoto/Isabel Mass)

 

 

 

ScienceDaily.com   —   Findings are rapidly expanding researchers’ understanding of a new class of brain cells — mirror neurons — which are active both when people perform an action and when they watch it being performed.

Some scientists speculate that a mirror system in people forms the basis for social behavior, for our ability to imitate, acquire language, and show empathy and understanding. It also may have played a role in the evolution of speech. Mirror neurons were so named because, by firing both when an animal acts and when it simply watches the same action, they were thought to “mirror” movement, as though the observer itself were acting.

Advances in the past few years have newly defined different types of mirror neurons in monkeys and shown how finely tuned these subsets of mirror neurons can be. New studies also have further characterized abnormal-as well as normal-mirror activity in the brains of children with the social communication disorder known as autism, suggesting new approaches to treatment.

“The tremendous excitement that has been generated in the field by the study of mirror neurons stems from the implications of the findings, which have led to numerous new hypotheses about behavior, human evolution, and neurodevelopmental disorders,” says Mahlon DeLong, MD, of Emory University School of Medicine.

Mirror neurons, a class of nerve cells in areas of the brain relaying signals for planning movement and carrying it out, were discovered 11 years ago, an offshoot of studies examining hand and mouth movements in monkeys. Mirror neuron research in the intervening years has expanded into a diverse array of fields. And the implications have been enormous, encompassing evolutionary development, theories of self and mind, and treatments for schizophrenia and stroke.

Findings being presented at Neuroscience 2007 include new research based on work in monkeys, showing that subsets of mirror neurons distinguish between observed actions carried out within hand’s reach and those beyond the animal’s personal space.

In his study, Peter Thier, PhD, at Tübingen University, first identified a group of mirror neurons by recording single nerve cell activity from electrodes when a monkey gripped different objects and when the monkey watched a person grasp the same objects, both nearby and farther away. About half of the nerve cells that were active when the monkey picked up the objects also sprung into action when it watched a person do so. Thier was assisted by research fellow Antonio Casile and PhD student Vittorio Caggiano, and worked closely with the lab of Giacomo Rizzolatti, MD, at the University of Parma.

They also noticed that some of these confirmed mirror neurons were active only when the monkey was watching activity within its personal space, defined as within reaching distance; others responded only to actions performed in a place outside the monkey’s grasp. Thier and colleagues recorded this preferential activity in 22 nerve cells, or together half of the mirror neurons. The other half of the mirror neurons showed activity that did not depend on how close the grasping action was to the monkey.

Although at this stage assigning a functional role is still speculation, Thier suggests this proximity-specific activity in mirror neurons may play an important role when we monitor what goes on around us, or serve as the basis for inferring the intentions of others and for cooperative behavior. “These neurons might encode actions of others that the observers might directly influence, or with which he or she can interact,” he says.

Other findings show that mirror neuron activity is instrumental for interpreting the facial expressions and actions of others but may not be sufficient for decoding their thoughts and intentions.

The studies examined changes in certain electroencephalograms (EEG) or brain wave patterns known as mu rhythms, which have a frequency of 8-13 hertz, or oscillations per second. Previous findings based on EEG recordings from the part of the brain that is directly involved in relaying signals for movement and sensing stimuli, known as the sensorimotor cortex, indicate that mu rhythms typically are suppressed by mirror activity in premotor areas of the brain. However, this does not happen in children with autism. As a result, the new work suggests, alternative strategies for reading faces and understanding others develop in the brains of these children.

Pursuing two parallel studies, Jaime Pineda, PhD, at the University of California, San Diego, aimed to contribute evidence supporting one of two theories about the ways we evaluate the actions and intentions of other people-either implicitly or through language-based theoretical concepts.

Using EEG recordings to examine patterns of brain wave activity, Pineda first worked with 23 adults, who were asked to look at photos showing just the eye region of people making various facial expressions. In three separate trials, the subjects were asked to identify either the emotion, race, or gender of the people in the photographs. In a subsequent task, subjects looked at three-panel cartoon strips and were asked to choose a fourth panel that completed the strip-either the conclusion of a series of physical actions or the result of a person interacting with an object. A sequence of a prisoner removing the window of his cell, then looking at his bed, for example, could be followed by a frame of the prisoner asleep, yawning, or using the bedsheet to make a rope. Answering correctly depended on interpreting the cartoon character’s intentions appropriately or understanding how physical objects interact.

Pineda repeated the studies with 28 children, 7 to 17 years old, half of whom had autism. The other half were typically developing children.

Recordings from the studies with adults showed a correlation between mu suppression, or mirror neuron activity, and accuracy for both tasks. In fact, the suppression of mu rhythms during the facial expression task also correlated with accuracy in the exercise with the cartoons, suggesting that reading people’s expressions and interpreting their intentions may draw from similar activity in the brain.

Recordings from the typically developing children showed similar patterns of suppression during the two tasks, indicating that mirror neuron activity is fully developed by age 7.

In contrast, recordings from the children with autism showed that mu rhythms were enhanced during both tasks. Enhancement is an indication that the mirror neuron system is disengaged. However, because the children still were able to perform the task, Pineda says, “we propose that children with autism develop alternative, non-mirror neuron-based coping strategies for understanding facial expressions and interpreting others’ mental states.” He suggests that “these compensatory strategies involve inhibition of residual mirror neuron functioning.”

These results could be applied to the development of treatments for autism. Pineda and his group have been using neurofeedback training to successfully renormalize functioning in this system. That is, they see mu suppression that is more characteristic of the typically developing brain following such training. “Our findings are consistent with the idea that mirror neurons are not absent in autism,” Pineda says, “but rather are abnormally responsive to stimuli and abnormally integrated into wider social-cognitive brain circuits.

“This idea implies that a retraining of mirror neurons to respond appropriately to stimuli and integrate normally into wider circuits may reduce the social symptoms of autism.”

Advances in recording brain activity also have made possible findings showing that mirror systems are active even when we are not observing an action with an eye to repeating it.

Suresh Muthukumaraswamy, PhD, at Cardiff University, found that the mirror system is activated when we watch specific actions, even when we are concentrating on a separate task.

The results are based on previous research showing that motor systems in the brain are activated when a person observes an action being performed and on interpretations suggesting that we understand and learn to imitate the actions of others through these brain mechanisms.

Working with 13 adults with an average age of 29, Muthukumaraswamy compared brain activity recorded via magnetoencephalography (MEG). This monitoring technique measures the weak magnetic fields emitted by nerve cells, and, recording from 275 locations, Muthukumaraswamy was able to monitor changes in activity every 600th of a second.

“Although MEG has been in existence for more than 20 years, recent advances in hardware, computing technology, and the algorithms used to analyze the data allow much more detailed analysis of brain function than was previously possible,” he says.

Brain activity was recorded as the subjects passively watched a sequence of finger movements, watched the movements knowing they would be asked to repeat them, added up the number of fingers moved as they watched, and performed the sequence of movements themselves.

Results from these recordings showed similar activity when the subjects performed the movement sequence and when they watched someone else do it. In addition, Muthukumaraswamy noted increased activity in areas of the brain regulating motor activity when subjects observed the movements knowing they would later do them, and when they added up the number of fingers used, compared with passive watching.

“These data suggest that activity of human mirror neuron systems is generally increased by attention relative to passive observation, even if that attention is not directed toward a specific motor activity,” says Muthukumaraswamy. “Our results suggest that the mirror system remains active regardless of any concurrent task and hence is probably an automatic system.

“A good scientific understanding of the properties of the mirror system in normal humans is important,” he adds, “because this may help to understand clinical disorders such as autism where the mirror system may not be functioning normally.”

Other findings based on EEG recordings provide the first evidence of normal mirror activity in children with autism: People familiar to children with autism may activate mirror areas of the brain in normal patterns when unfamiliar people do not.

Previous research has shown that mu rhythms are suppressed when a subject identifies with an active person being observed. Based on this work, Lindsay Oberman, PhD, at the University of California, San Diego, examined the role of two separate factors in the mirror system response of children with autism.

Six videos were shown to a group of 26 boys, 8 to 12 years old; half had autism. Three videos showed images representing varying degrees of social interaction: two bouncing balls (the baseline measurement), three people tossing a ball to themselves, and three people throwing the ball to each other and off the screen to the viewer. The other set of videos showed people with varying degrees of familiarity to the subjects: strangers opening and closing their hand, family members making the same hand movement, and the subjects themselves doing the same.

EEG recordings from 13 electrodes in a cap showed that mu activity was suppressed most when subjects watched videos of themselves, indicating the greatest mirror neuron activity. For both groups, the measurements showed a slightly lower level of suppression when subjects watched familiar people in the video and the least when watching strangers. This indicates that normal mirror neuron activity was evoked when children with autism watched family members, but not strangers.

“Thus, to say that the mirror neuron system is nonfunctional may only be partially correct,” says Oberman. “Perhaps individuals with autism have fewer mirror neurons and/or less functional mirror neurons that require a greater degree of activation than a typical child’s system in order to respond.”

The mirror neuron system may react to stimuli that the observer sees as “like me.” If this is the case, suggests Oberman, “perhaps typical individuals apply this identification to all people (both familiar and unfamiliar), resulting in activation of these areas in response to the observed stimuli, while individuals on the autism spectrum only consider familiar individuals (including themselves) as ‘like me,’ ” she says.

This evidence for normal mirror neuron activity in autistic children may indicate that mirror system dysfunction in these cases reflects an impairment in identifying with and assigning personal significance to unfamiliar people and things, Oberman suggests. Whether deficits in relating to unfamiliar people that are characteristic of autism are the cause or the result of a dysfunctional mirror neuron system is unclear.

Source: Society For Neuroscience