What are the ventral and dorsal flow?

The visual system can be divided into two flows, the ventral flow and the dorsal flow. The ventral flow is for object perception, while the dorsal flow is for space perception. New theories have now been developed that elaborate these flows both anatomically and functionally.

• For example the perception-action model. This defines the dorsal flow as responsible for unconscious visual action guidance and the ventral flow as responsible for conscious perception.

• A tripartite division has also been proposed for the dorsal flow to explain the variety of visuospatial functions. The three pathways start in the posterior parietal cortex and mediate different visuospatial skills. The first path is the parieto-premotor path for eye movements, various forms of visual action guidance and grasping. The second path is the parieto-prefrontal path for top-down control of eye movements and spatial working memory. The third path is the parieto-medial temporal path for spatial skills related to navigation.

Is there hemispheric dominance?

The scientific evidence for hemispheric dominance with regard to object perception and object recognition is contradictory. Some studies conclude a right-half dominance, and others a left-half dominance. There are also researchers who do not assume that one of the hemispheres of the brain would be more dominant, but who look at object recognition as involving hierarchically organised processes that depend on either the left or right hemisphere. They argue that the right half specialises in distinguishing general characteristics, while the left half specialises in assigning meaning to objects for categorisation and recognition. There is consensus within the scientific world that the right hemisphere dominates with regard to visuospatial attention.

What is the Visual Object and Space Perception battery?

The VOSP consists of eight tests designed to each assess a certain aspect of the object or space perception, while minimising the involvement of other cognitive skills. This test is used here to investigate the neural underpinnings of object and space perception in patients with profound traumatic brain injury. 

What can be concluded about the dominance of the left and right hemispheres of object and space perception?

The research provides evidence that supports the existence of a functional subdivision of the visual system. For example, it is confirmed that the left half is involved in object perception and the right half is involved in space perception. However, the results also showed different hemispheric dominance for the ventral and dorsal flow, but that does not mean that they do not interact with each other. The data also supports the existence of a hierarchical organization of the ventral flow and the complementary role of both hemispheres in object recognition. Unfortunately, there are also limitations to this research, for example, that the brain damage among the participants has already occurred many years ago and there may be functional recovery. CT scans were also used instead of MRI and these have a lower resolution and are less able to distinguish between gray and white matter.

The specific neurobiological characteristics of autism are manifest in hypoactivation of the motor system during action word comprehension. Previous literature suggests a functional importance of this area for action semantic processing, as well as structural abnormalities in autism in frontal motor systems, their internal connections, and those connecting them to other brain regions (particularly the long-distance pathways between temporal and parietal circuits involved in perception and frontal and motor circuits important for action processing). The developing circuits binding action- with perception-related information are fragile in autism and do not efficiently channel perceptual information to motor circuits.

What is ‘embodied’ or ‘grounded’ cognition?

Embodied cognition is a framework that states that conceptual thought and retrieval of meaning involves the complete or partial reactivation, in a simulative manner, of neural sensorimotor activation experienced during initial concept acquisition. Neural substrates for thought, language, and movement are intrinsically interwoven and functionally interdependent.

How is language connected to the human motor system?

Sounds, spoken and written words with action-related meaning produce somatotopic semantic activation of the human motor system. Neural control of movement includes many cortical and subcortical regions along with the cerebellum, most of which have been seen to be activated by words with action affordances.

What evidence is there to support that activity in certain regions indexes semantic processing rather than reflecting post-comprehension thought processes?

• Motor system activation whilst processing action-related stimuli is manifest even if participants do not actively attend to language input.
• Motor activation during processing of language is flexible and follows the pattern that is expected for semantic mechanisms.
• Overt movement of stimulation of motor areas has a causal effect on simultaneous processing of specific types of action words, and also word processing may impact on specific motor mechanisms with effects visible in behavior and electrophysiological brain recordings.
• Frontocentral activity emerges in the semantic learning of new action words. 
• Movement disorders and clinical impairments to motor systems are associated with specific processing impairments or abnormalities for action-related words which call on action knowledge in their meaning retrieval.

What is autism (viewed as a movement disorder)?

Autism spectrum conditions (ASC) are neurodevelopmental syndromes characterized by impairments in social interaction, communication and language, repetitive behaviors and intense, rigid interests. A neurobiological perspective emphasizes a possible deviance in action perception integration. The autistic phenotype is an emergent property of developmental interactions between many brain regions and functions. It is possible that the normal developmental trajectory has gone wrong, and early motor disruption derailed multiple domains where autistic symptomatology emerges.

Does motor dysfunction in autism occur more often than in the general population and what kind of motor deficits do they have?

Individuals with autisms show poorer motor coordination, arm movements, gait, postural stability, slower repetitive movements, overflow, gait, balance, manual dexterity and coordination, dysrhythmia, ball skills, grip strength, finger tapping, and pegboard tasks. The most common types of errors that autistic people make, are needing more attempts, only partially replicating actions, showing abnormal synkinesias, using part of the body as an object, orienting the hand incorrectly, or misjudging the amplitude, force or size of gestures. These are all spatial errors, instead of problems with recognition and representing actions and gestures. It may be that motor deficit in autism isn´t related to the actual execution of the movement, but instead to the preparation and planning and programming of movements.

How does the corticol motor system relate to movement impairment?

The corticol motor system (primary motor, premotor, and supplementary motor cortex) shows differences between children with and without autism. Individuals with autism show increased grey matter volume and surface area in the right motor cortex, as well as an excess in white matter in M1. They appear to show a difference in functional connectivity, whereby during a movement task, synchronized activity between left and right M1 and between M1 and other motor regions is reduced.

How does self-other mapping relate to autism?

Imitation deficits can be described in terms of impairments in self-other mapping. Self-other mapping is the ability to connect an observed action with the motor program necessary to perform a similar movement oneself. The mechanism of this perception-to-action mapping is posited in mirror neurons, which are responsive both when a specific action is carried out and when the same action is perceived visually or acoustically. Neural activity attributable to mirror neurons in the premotor and motor cortex is much lower in individuals with autism.

What is the broken mirror hypothesis?

The broken mirror theory claims that a dysfunction of the mirror neuron system may be the cause of poor social interaction and cognition in individuals with autism. Individuals with autism show a lack of mirror neuron activity in several regions of the brain. Mirror neurons may enable humans to see themselves as others see them, which may be essential for self-awareness and introspection. A dysfunctional mirror neuron system can create an absence of empathy, language deficits, poor imitation, and other symptoms of ASC.

How does language and motor development relate to later autism?

In autism, the relationship between motor skills in toddlerhood and receptive and expressive language in childhood is mediated by reduced exploration of objects and environment and reduced social interest. Motor skills such as babbling, shuffling, and crawling all alter an infant´s relationship with the objects and people around him or her and provides new learning experiences and promotes language development. It is then expected that early motoric dysfunction leads to language delays and other abnormalities that are characteristic for autism.

How do cells within action perception circuits become infused with multimodal sensorimotor properties?

Associative learning and linkage with other neural populations, also referred to as information mixing, refers to the finding of multimodal neurons which carry information across different modalities, including motor, visual, and auditory feature processing. Action perception integration happens when sensory and motor populations of neurons increase the efficacy of their mutual connections due to correlated activity. The stronger links provide additional recurrent activation in action production and the perception process and yield activity maintenance after stimulation, due to reverberant activation supported by the strong population-internal links.

How can the specific neurobiological characteristics of autism be regarded as a plausible cause of the efficiency reduction in action semantic processing?

The specific neurobiological characteristics of autism are manifest in hypoactivation of the motor system during action word comprehension. Previous literature suggests a functional importance of this area for action semantic processing, as well as structural abnormalities in autism in frontal motor systems, their internal connections, and those connecting them to other brain regions (particularly the long-distance pathways between temporal and parietal circuits involved in perception and frontal and motor circuits important for action processing). The developing circuits binding action- with perception-related information are fragile in autism and do not efficiently channel perceptual information to motor circuits.

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