The ventral stream is an important part of the brain. Although the brain is divided into various regions, the different parts work together to achieve complicated processes. Vision is one example of a highly complex series of processes involving information passing through different brain regions. But what links these brain regions, how is the information divided, and where is it processed?
The ventral stream is an essential neurological pathway that carries information from the primary visual cortex to the inferior temporal lobe and other important structures. Information processing takes place pertaining to what the item is, its shape, and assisting in memory forming.
The ventral stream is essential for interpreting optical stimuli. Without it, the organism would be unable to see effectively. However, the ventral stream forms part of a greater system that processes visual information. Below we’ll investigate how it works, what it connects to, complications to the system, and other aspects.
The Physical Characteristics Of The Ventral StreamThe Function And Location Of The Ventral StreamComplications Of The Ventral StreamConclusion
The Physical Characteristics Of The Ventral Stream
The Function And Location Of The Ventral Stream
Complications Of The Ventral Stream
Conclusion
Theventral streamis also known as the“vision-for-perception” pathwayor the ventral visual pathway. It isone of twopathways leading from the brain region known as thestriate cortex.
The ventral stream/pathway, along with the dorsal visual pathway, is a“large” fiber bundleofmultisynaptic connections.
The ventral stream’s main " highway " is theinferior longitudinal fasciculus. This elongated fiber bundle is composed ofwhite matter (axons).
The ventral stream is one of manyinformation highways in the brain. It is one of two describedpathwaysthattakessensory informationfrom the primary visual cortex to other brain regions.
The ventral stream carries information to thetemporal lobeand areas of theoccipital lobesurrounding the primary visual cortex.
Theventral stream’s informationallows the brain toidentifyandrecognizewhat the eye looks at (one reason the ventral stream is often called the“what”pathway).
Thedorsal streamis the“where” pathway. This pathway runs across the top of the brain to the parietal lobe and allows the brain to process information relating tospatial relationshipsbetween objects and their movement.
Thesesystems function togetherto help the brain process what the organism looks at and where it fits in time and space according to the surrounding environment.
There are stillmany uncertaintiesconcerning the exact function of each step in the network.One of the areas of uncertainty iswhether theventral stream connects to the parietal lobethrough other connecting pathways.
Researchers believe the ventral stream is necessary formemory, recognition, and consciousperception.
Where Is The Ventral Stream Located?
The ventral stream is a cortical pathway (in the brain) connecting different lobes. “Ventral” refers to thebottom area, and in this case, of thebrain.
The ventral stream stretches from theprimary visual cortexon the occipital lobe to theextrastriate areassurrounding the primary visual cortex (the areas of the occipital cortex that assist with processing vision) and to theinferior part of the temporal lobe.
The primary visual cortex is referred to as the"striate" because Gennari’s stria characterize area. These striae areprominent bandsofmyelinated axonsthat appear as “striped or banded.” Cells in this area have alaminar cell structure.
Both occipital lobes contain acalcarine sulcusalong its medial surface. Within this calcarine sulcus, we find thestriate cortex, which makes up around 10% of the brain.
The ventral pathway passes through theoccipitotemporal cortex. Researchers believe that it mightextendinto theventrolateral prefrontal cortexas well.
Aside from the primary visual cortex (V1) and the temporal lobe, the ventral stream passes optical information to thesecondary visual cortex, or prestriate cortex (V2), andvisual area 4(V4).
How The Ventral Stream Works
The ventral stream works aspart of a systemin the brain to process visual stimuli (i.e., what the eye sees) and gains meaning and understanding. This processing of visual information occurs across several areas of the brain.
Visual stimuli enter through theretinaand travel along theoptic nervesuntil it reaches the lateral geniculate nucleusinside thethalamus(think of catching different trains at various stations which make up the various legs of a journey).
Once at the thalamus, the optical information takesone of three “train lines”(pathways).
The information then “transfers” to theoptical radiation, a tract (pathway) thatloops aroundthe lateral ventricle in both cerebral hemispheres. This leg of the journeyterminatesin theoccipital lobe, specifically at theprimary visual cortex (V1).
The optic radiation’s axons (and axon terminals) transport thespecific informationfrom thevisual fieldto the related parts of theprimary visual cortex(V1). I.e., The parts of the V1 that deal withcolor receive colorinformation, those dealing withshape receive shape, etc.
This process ofsorting and deliveringspecific information to a specific region within the brain is known asretinotopy.
Information pertinent to theinferior visual fieldpasses through axons that terminateabovethecalcarine sulcusof the primary visual cortex. Conversely, information concerning thesuperiorportion of thevisual fieldtravels through axons that terminatebelowthecalcarine sulcus.
The various neurons making up the V1 area of the occipital lobe arearranged into columnsof similar neurons according to their function. I.e., neurons responsible for processing orientational information from the contralateral eye are grouped.
Neurons receiving similar information from the ipsilateral eye are grouped inseparate columns.
Each modulebuilds a small“pieceof the visual puzzle,” whichworks togetherto generate the “whole” picture.
The processing of visual stimuli is not limited to theprimary visual cortex. The areas surrounding this region are called theextrastriate cortex(still within the occipital lobe), and they play a fundamental role inanalyzing opticalinformation.
The ventral stream becomes relevant at this junction. As the sensory informationenters the V1, the ventral stream is responsible forrelaying it to the extrastriate regionsand eventually to thetemporal lobe.
Itsfunctionalityis directly related to thenumber of connectionsthe ventral stream makes within the brain (like a highway, with many roads branching off to the various regions).
The ventral stream is anetwork of connectionswithin the occipitotemporal regions that links the primary visual cortex tospecialized cortical and subcortical structures.These structures arecritical foremotions, habit-forming, learning, and long and short memory forming and recalling.
Unlike the dorsal stream (which deals with dynamic relationships between items), the facilities connected to the ventral stream aregeared toward stable visual stimuliandcreating associationswith them. These associations are known as “the processing ofobject quality.”
However, there is adegree of overlap.I.e., spatial information from the dorsal stream flows to the same “stations” connected to the ventral stream. This overlap in information processingallows the braintomore fully comprehendwhat the organism is looking at.
The ventral streamconnects to at least six cortical and subcortical regionsalong its length. All of these pathways contribute to processing object quality.
Researchers believe that the information isnot limited to movement in one directionbut rather acomplex network of feedback and forward loopsthat allow the various connections to communicate.
Once in the ventral stream, the information moves to theV2 and the V4. TheV2area is fundamentally a morerefined version of V1. If V1 is where the information is sorted, V2 is where the information goes to befurther processed, particularly patterns.
TheV4area of the brain is important for processingcolorand other aspects. There are still manyknowledge gapsregarding the V4’s function.
After passing through the various connections along the pathway, the ventral stream links with the temporal lobe, specifically at theanterior inferior temporal cortex.
Scientists believe that this region of the brainfurther processes complex shapes. The temporal lobe is alsoimportant regarding memories.
Why The Ventral Stream Is Important
Without the ventral stream, the braincould not process optic information, particularly when recognizing and identifying objects.
Thebrain processesedges, simple shapes, contours, and colors in the primary visual cortex and surrounding areas. The inferior temporal cortex is important forprocessing complex shapes.
Withoutthe connection via the ventral stream, theorganism would not effectively processwhatever they were looking at.
Without the compartmentalization of information, the brain would be unable to quickly form an understanding, a delay that could havelife or death consequencesfor the organism.
The ventral stream is implicitly linked to the organism’s visual capabilities. If the pathway, or regions of the brain that it connects to,sustain damage, it mayimpair or completely cut off the organism’s vision.
Some of theeffects of damagingthese regions of the brain lead to:
Damage to these regions of the brain is eitherthrough trauma or disease.
Lesions On The Occipital/Temporal Lobe, Or Along The Pathway
Lesions are anydamage the brain sustainsthroughdisease, genetics, or trauma. Lesions may start as asymptomatic and then later develop symptoms.
Lesionsto the ventral stream result in theloss of discriminatoryidentificationandrecognitionfunctions.
Sometypical symptomsof brain lesions include:
Wherethe lesion is in the brain willdetermine its treatment plan. Most critical is that you shouldseek medical adviceif you suspect lesions.
The Effects Of Alzheimer’s Disease On The Ventral Stream
Alzheimer’sis adegenerative diseasethat attacks parts of the brain,causinglossof function, cognitive ability, and motor skills, among others.
The patient loses sight when Alzheimer’s disease attacks visually orientated brain cells (atrophy). The cortex of the braindealing with memoryis also affected.
Although the mechanics of what causes Alzheimer’s are not fully understood, scientists believe that the disease isdue to proteins not functioning properly, which has a knock-on effect on the synapses in the brain.
There is usually aplaque build-upin the brain. These aggregations create atoxic effecton the brain where they are found.
Thesymptomsof Alzheimer’s disease include:
Although there isno cure for Alzheimer’s, many people manage their symptoms with medication.
The Effects Of Trauma On The Ventral Stream
Trauma is a severe cause ofmany issuesrelating to the brain and vision. Trauma occurs inmany shapes and formsand has varying effects under different circumstances.
When subjected to visual stimuli, scientists discovered that those suffering from PTSD hadlessened activity in the ventral stream(and associated areas).
Physical damage(trauma) can alsoinhibit the ventral streamand surrounding areas from functioning properly.
The brain is an important network of neurons and their various parts, working in unison to produce a functional organism. The ventral stream is part of this network, linking the visual processing areas of the occipital lobe to the memory-orientated temporal lobe. The ventral stream is critical for effective analysis of the visual field, and damages to this pathway (via disease and trauma) result in a loss of vision in the organism.
References
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3532569/
https://pubmed.ncbi.nlm.nih.gov/22810517/
https://pubmed.ncbi.nlm.nih.gov/15265653/
https://www.ncbi.nlm.nih.gov/books/NBK482504/
https://www.sciencedirect.com/topics/neuroscience/retinotopy
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