Neural binding

Neural binding is the neuroscientific aspect of what is commonly known as the

The study of the binding problem in neuroscience stems from the much older psychological study of the binding phenomenon, which has its roots in the ancient philosophical study of the same problems. Today, there is a close interplay between neuroscience and psychology, which is especially relevant to neural binding.

Gestalt psychology and correlating critiques

Gestalt psychology is a field that has been intertwined with neural binding due to its advances in conceptualizing how the brain views objects, reacts to stimuli, and then reacts on a global level. Since Gestalt Psychology has become so involved, “grouping” has become an important part of understanding neural binding. The scientists that supported this theory were solely focused on the idea that mechanisms in the brain operated preattentively.

"Grouping" has become especially important for neural binding due to studies in

Later, more writings were produced regarding preattentive binding. Although they did not focus as much on Gestalt psychology, they were important to the idea of the preattentiveness of the brain. One such addition onto this theory was put out by Duncan and Humphreys. They said that some types of features, when trying to form the image, compete against one another for "the limited capacity object recognition stage". This means that certain parts of an object have multiple ways of being featured by the brain. Each different type of feature then competes with the others, trying to become the feature that is displayed to the individual. This can then account for the understanding of how each person views a whole object differently than another person. They also then see its global function on a very different scale.[5]

This idea of differential grouping is also brought up by Aksentijevic, Elliott, and Barber. Their theory is based on different perceptions of geometrical space that can then supply a "starting point for a systematic exploration of the subjective properties of certain classes of visual and auditory grouping phenomena, such as apparent motion, grouping within static two-dimensional displays and auditory streaming." This idea shows how different people perceive geometrical space, which can lead to different auditory and visual streams.^[5]

Proposed models

Temporal

The Temporal Binding Hypothesis has a history in neuroscience which spans back to at least the early 1980s. Christoph Von der Malsburg proposed that neurons carry two distinct signals, one of conventional rate code in relation to the ‘effectiveness’ of the feature it is encoding and another which is conveyed in terms of spike coordination between assemblies of neurons.^[6] A decade later Francis Crick & Christof Koch developed the model further by explaining the synchronization of distant neurons by transient gamma wave oscillations being guided by attention.^[7] By 1995, Francisco Varela had established the importance of the role of the oscillatory phase in the pairing of neuron assemblies.^[8]

The Temporal Binding Hypothesis was first proposed as a way of addressing the combinatorial problem of neural binding, which emphasizes the impossibly large number of connections that would have to be made between neurons of overlapping function and association in order to achieve the degree of observable complexity in neural binding. Modern models that are currently being developed often retain the structure of temporal synchrony due to this significant advantage as well as the strong experimental support for the existence of global brain oscillations.

Gamma band activity

It has been widely observed that distributed collections of neurons oscillate within the gamma band of frequencies (typically between 30–80 Hz)..

Phasic pairing mechanisms

Varela’s model describes the selection of cellular assemblies, sometimes referred to as resonant or reverberating (

Criticism

The temporal binding models have been criticized by some for being unwarranted in their far-reaching speculative nature.^[9] This claim is usually made in favor of a more classical model of neural function.

Quantum models

Some more recent models have incorporated quantum theory as a component of the underlying neural dynamics behind binding due to the strong explanatory power of quantum mechanics and their claim of the insufficiency of current models for explaining the complexity of the binding mechanism.

In 2001, da Rocha developed a model which utilized the basic structure of the Temporal Binding Hypothesis, with global

A neural signaling mechanism in certain catecholaminergic neurons has been hypothesized that uses quantum mechanical electron transport (Catecholaminergic Neuron Electron Transport, or CNET).[10]^[11][12] The hypothesis is based in part on the observation by many independent researchers that electron tunneling occurs in ferritin (an iron storage protein that is prevalent in those neurons) at room temperature and ambient conditions.^{[13][14][15][16]} The function of this mechanism would be to assist in action selection, but the mechanism itself would be capable of integrating millions of cognitive and sensory neural signals, using a physical mechanism associated with strong electron-electron interactions.  The hypothesis predicted a number of physical properties of these neurons that have been subsequently observed experimentally, such as electron tunneling in substantia nigra pars compacta (SNc) tissue and the presence of disordered arrays of ferritin in SNc tissue.^[17][18][19] The hypothesis also predicted that disordered ferritin arrays like those found in SNc tissue should be capable of supporting long-range electron transport and providing a switching or routing function, both of which have been subsequently observed.^[20][21][22]

CNET also predicted that the largest SNc neurons should mediate action selection. This prediction was contrary to earlier proposals about the function of those neurons that were based on predictive reward dopamine signaling.^[23][24] However, a team led by Dr. Pascal Kaiser of Harvard Medical School subsequently demonstrated that those neurons code movement, consistent with the earlier predictions of CNET.^[25] While the CNET mechanism has not yet been directly observed, it may be possible to do so using quantum dot fluorophores tagged to ferritin or other analytical techniques for detecting electron tunneling.^[26]

Non-synchronous models

Many non-temporal theories attempt to retain a more classical conception of neuron signaling based on

These models can be vulnerable to the combinatorial and connectivity problems, which come as a natural consequence of depending solely on one-to-one communication of conventional information via spike rate coding. These models also require the seamless directing and combining of signals, which either assumes a controller (proposed to be the pulvinar nuclei^[27]) or a mechanism for the spontaneous self-assembly of neural ensembles.

Test cases

Sensory

Much of the experimental evidence for neural binding has traditionally revolved around sensory awareness. Sensory awareness is accomplished by integrating things together by cognitively perceiving them and then segmenting them so that, in total, there is an image created. Since there can be an infinite number of possibilities in the perception of an object, this has been a unique area of study. The way the brain then collectively pieces certain things together via networking is important not only in the global way of perceiving but also in segmentation. Much of sensory awareness has to do with the taking of a single piece of an object's makeup and then binding its total characteristics so that the brain perceives the object in its final form. Much of the research for the understanding of segmentation and how the brain perceives an object has been done by studying cats. A major finding of this research has to do with the understanding of

Francis Crick and Christof Koch proposed that specific neural activity can stimulate short-term memory, forming a continuous and dynamic consciousness.

Cognitive binding is associated with the different states of human

The thalamus and cortex are important anatomical features in cognitive and sensory awareness. The understanding of how these neurons fire and relate to one other in each of these states (REM and Waking) is paramount to understanding awareness and its relation to neural binding.

In the waking state, neuronal activity in animals is subject to changes based on the current environment. Changes in environment act as a form of stress on the brain so that when sensory neurons are then fired synchronously, they acclimate to the new state. This new state can then be moved to the

The pairing of these oscillations can then help input the correct sensory material. If these paired oscillations are not new, then cognitively these firings will be easily understood. If there are new firings, the brain will have to acclimate to the new understanding.[30]

In REM sleep, the only extreme difference from the waking state is that the brain does not have the actual waking amount of sensory firings, so cognitively, there is not as much awareness here, although the activity of the "brain’s eye" is still quite significant and very similar to the waking state. Studies have shown that during sleep there are still 40 Hz Oscillation firings. These firings are due to the perceived stimuli happening in dreams. "^[30]

Learning/memory

Opitz argues that the binding of different brain areas is mediated by the hippocampus. Relational bindings, or relationships between separate objects, concepts, and memories, are very flexible because the targets can be combined in so many different ways to deal with the present situation, and the hippocampus ensures that these parts are arranged into a coherent whole.^[31] Particularly, the hippocampus has been implicated in binding that is involved with episodic memory, working memory, and language acquisition. According to Opitz, this is viable because the hippocampus meets all criteria to be suitable for the regulation relational binding and, based on its patterns of activity, it is likely that it is involved.

Clinical implications

Autism

Several researchers have suggested a clinical link between difficulties in neural binding and autism spectrum disorders.^[32] It has been postulated that there is a level of underconnectivity between certain areas of the autistic brain, specifically those areas that involve social cognition. They also hypothesize that there may be overconnectivity within certain neuronal cell assemblies. Researchers have suggested that these issues with coherence of neural networks give rise to the hallmark autistic symptoms, namely, impaired social cognition/interactions and repetitive behaviors.

There is one major piece of evidence suggesting that abnormal connectivity occurs in autism. Autistic brains are known to develop very rapidly early in life, and this could cause problems in the development of cortical connections. It has been suggested that this early overdevelopment may be a cause for the impaired connectivity in autism.

It is also possible that problems with binding give way to the fractured mental state that is characteristic of schizophrenia. Schizophrenic patients experience a “disintegration of consciousness” which involves hallucinations, delusions, and generally disordered thinking. It is hypothesized that this mental disorganization is caused by underlying neural disorganization due to disordered binding, which is then further complicated by the occurrence of complex mental processes in this disordered state.^[33] This can essentially be viewed as a pathological rise in the neural complexity of the brain. The dissociative symptoms and disorganized speech associated with schizophrenia are consistent with this idea. It is also possible that disordered binding between the regulatory mechanisms of the brain gives rise to a lack of synchronized activation of its neural networks.

Anesthesia

A deeper understanding of the mechanisms underlying consciousness on the

• Binding problem
• Binding neuron
• Recurrent thalamo-cortical resonance
• Hard Problem of Consciousness
• Consciousness
• Attention

References