The inferior temporal gyrus is one of three
gyri
In neuroanatomy, a gyrus (pl. gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; sg. ''sulcus''). Gyri and sulci create the folded appearance of the brain in humans and other ma ...
of the
temporal lobe
The temporal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe ...
and is located below the
middle temporal gyrus
Middle temporal gyrus is a gyrus in the brain on the temporal lobe. It is located between the superior temporal gyrus and inferior temporal gyrus. It corresponds largely to Brodmann area 21.
The middle temporal gyrus is bounded by:
* the superi ...
, connected behind with the
inferior occipital gyrus; it also extends around the infero-lateral border on to the inferior surface of the
temporal lobe
The temporal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe ...
, where it is limited by the inferior
sulcus. This region is one of the higher levels of the
ventral stream
The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual ...
of visual processing, associated with the representation of objects, places, faces, and colors. It may also be involved in face perception, and in the recognition of numbers and words.
The inferior temporal gyrus is the anterior region of the
temporal lobe
The temporal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe ...
located underneath the central temporal sulcus. The primary function of the occipital temporal gyrus – otherwise referenced as IT cortex – is associated with visual stimuli processing, namely visual object recognition, and has been suggested by recent experimental results as the final location of the ventral cortical visual system.
The IT cortex in humans is also known as the Inferior Temporal Gyrus since it has been located to a specific region of the human temporal lobe. The IT processes visual stimuli of objects in our
field of vision
The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...
, and is involved with memory and memory recall to identify that object; it is involved with the processing and perception created by visual stimuli amplified in the V1, V2, V3, and V4 regions of the
occipital lobe
The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head".
The occipital lobe is the vi ...
. This region processes the color and form of the object in the visual field and is responsible for producing the “what” from this visual stimuli, or in other words identifying the object based on the color and form of the object and comparing that processed information to stored memories of objects to identify that object.
The IT cortex's neurological significance is not just its contribution to the processing of visual stimuli in object recognition but also has been found to be a vital area with regards to simple processing of the
visual field
The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...
, difficulties with perceptual tasks and
spatial awareness
Spatial contextual awareness consociates contextual information such as an individual's or sensor's location, activity, the time of day, and proximity to other people or objects and devices.Chen, Guanling, and David Kotz. 2000. A Survey of Context- ...
, and the location of unique single cells that possibly explain the IT cortex's relation to memory.
Structure
![TempCapts](https://upload.wikimedia.org/wikipedia/commons/6/61/TempCapts.png)
The temporal lobe is unique to
primates
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...
. In humans, the IT cortex is more complex than their relative primate counterparts. The human inferior temporal cortex consists of the inferior temporal gyrus, the
middle temporal gyrus
Middle temporal gyrus is a gyrus in the brain on the temporal lobe. It is located between the superior temporal gyrus and inferior temporal gyrus. It corresponds largely to Brodmann area 21.
The middle temporal gyrus is bounded by:
* the superi ...
, and the
fusiform gyrus
The fusiform gyrus, also known as the ''lateral occipitotemporal gyrus'','' ''is part of the temporal lobe and occipital lobe in Brodmann area 37. The fusiform gyrus is located between the lingual gyrus and parahippocampal gyrus above, and the inf ...
. When looking at the brain laterally – that is from the side and looking at the surface of the temporal lobe – the inferior temporal gyrus is along the bottom portion of the temporal lobe, and is separated from the middle temporal gyrus located directly above by the
inferior temporal sulcus. Additionally, some processing of the visual field that corresponds to the
ventral stream
The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual ...
of visual processing occurs in the lower portion of the superior temporal gyrus closest to the superior temporal sulcus. The medial and ventral view of the brain – meaning looking at the medial surface from below the brain, facing upwards – reveals that the inferior temporal gyrus is separated from the fusiform gyrus by the occipital-temporal sulcus. This human inferior temporal cortex is much more complex than that of other primates: non-human primates have an inferior temporal cortex that is not divided into unique regions such as humans' inferior temporal gyrus, fusiform gyrus, or middle temporal gyrus.
This region of the brain corresponds to the inferior temporal cortex and is responsible for visual object recognition and receives processed visual information. The inferior temporal cortex in primates has specific regions dedicated to processing different visual stimuli processed and organized by the different layers of the
striate cortex
The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...
and extra-striate cortex. The information from the V1 –V5 regions of the
geniculate and tectopulvinar pathways are radiated to the IT cortex via the ventral stream: visual information specifically related to the color and form of the visual stimuli. Through comparative research between primates – humans and non-human primates – results indicate that the IT cortex plays a significant role in visual shape processing. This is supported by functional magnetic resonance imaging
(fMRI) data collected by researchers comparing this neurological process between humans and macaques.
Function
Receiving information
The light energy that comes from the rays bouncing off of an object is converted into chemical energy by the cells in the
retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
of the eye. This chemical energy is then converted into action potentials that are transferred through the
optic nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve i ...
and across the
optic chiasm
In neuroanatomy, the optic chiasm, or optic chiasma (; , ), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebrate ...
, where it is first processed by the
lateral geniculate nucleus
In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projec ...
of the thalamus. From there the information is sent to the
primary visual cortex
The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...
, region V1. It then travels from the visual areas in the
occipital lobe
The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head".
The occipital lobe is the vi ...
to the parietal and temporal lobes via two distinct anatomical streams. These two cortical visual systems were classified by Ungerleider and Mishkin (1982, see
two-streams hypothesis
The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visu ...
). One stream travels ventrally to the inferior temporal cortex (from V1 to V2 then through V4 to ITC) while the other travels dorsally to the posterior parietal cortex. They are labeled the “what” and “where” streams, respectively. The Inferior Temporal Cortex receives information from the
ventral stream
The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual ...
, understandably so, as it is known to be a region essential in recognizing patterns, faces, and objects.
Single-cell function in the inferior temporal gyrus
The understanding at the single-cell level of the IT cortex and its role of utilizing memory to identify objects and or process the visual field based on color and form visual information is a relatively recent in neuroscience. Early research indicated that the cellular connections of the temporal lobe to other memory associated areas of the brain – namely the
hippocampus
The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
, the
amygdala
The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...
, the
prefrontal cortex
In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA46, ...
, among others. These cellular connections have recently been found to explain unique elements of memory, suggesting that unique single-cells can be linked to specific unique types and even specific memories.
Research into the single-cell understanding of the IT cortex reveals many compelling characteristics of these cells: single-cells with similar selectivity of memory are clustered together across the cortical layers of the IT cortex; the temporal lobe neurons have recently been shown to display learning behaviors and possibly relate to
long-term memory
Long-term memory (LTM) is the stage of the Atkinson–Shiffrin memory model in which informative knowledge is held indefinitely. It is defined in contrast to short-term and working memory, which persist for only about 18 to 30 seconds. Long-t ...
; and, cortical memory within the IT cortex is likely to be enhanced over time thanks to the influence of the afferent-neurons of the medial-temporal region.
Further research of the single-cells of the IT cortex suggests that these cells not only have a direct link to the visual system pathway but also are deliberate in the visual stimuli they respond to: in certain cases, the single-cell IT cortex neurons do not initiate responses when spots or slits, namely simple visual stimuli, are present in the visual field; however, when complicated objects are put in place, this initiates a response in the single-cell neurons of the IT cortex. This provides evidence that not only are the single-cell neurons of the IT cortex related in having a unique specific response to visual stimuli but rather that each individual single-cell neuron has a specific response to a specific stimuli. The same study also reveals how the magnitude of the response of these single-cell neurons of the IT cortex do not change due to color and size but are only influenced by the shape. This led to even more interesting observations where specific IT neurons have been linked to the recognition of faces and hands. This is very interesting as to the possibility of relating to neurological disorders of prosopagnosia and explaining the complexity and interest in the human hand. Additional research from this study goes into more depth on the role of "face neurons" and "hand neurons" involved in the IT cortex.
The significance of the single-cell function in the IT cortex is that it is another pathway in addition to the lateral geniculate pathway that processes most visual system: this raises questions about how does it benefit our visual information processing in addition to normal visual pathways and what other functional units are involved in additional visual information processing.
Information processing
The information for color and form comes from P-cells that receive their information mainly from
cones
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex.
A cone is formed by a set of line segments, half-lines, or lines conn ...
, so they are sensitive to differences in form and color, as opposed to the M-cells that receive information about motion mainly from
rods. The neurons in the inferior temporal cortex, also called the inferior temporal visual association cortex, process this information from the P-cells. The
neurons
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
in the ITC have several unique properties that offer an explanation as to why this area is essential in recognizing patterns. They only respond to visual stimuli and their receptive fields always include the
fovea
Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure.
Human anatomy
*Fovea centralis of the retina
* Fovea buccalis or Dimple
* Fovea of the femoral head
* Trochlear fovea of the fr ...
, which is one of the densest areas of the retina and is responsible for acute central vision. These
receptive fields
The receptive field, or sensory space, is a delimited medium where some Stimulus (physiology), physiological stimuli can evoke a Sensory neuron, sensory neuronal response in specific organisms.
Complexity of the receptive field ranges from the un ...
tend to be larger than those in the
striate cortex
The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...
and often extend across the midline to unite the two visual half fields for the first time. IT neurons are selective for shape and/or color of stimulus and are usually more responsive to complex shapes as opposed to simple ones. A small percentage of them are selective for specific parts of the face. Faces and likely other complex shapes are seemingly coded by a sequence of activity across a group of cells, and IT cells can display both short or long-term memory for visual stimuli based on experience.
Object recognition
There are a number of regions within the ITC that work together for processing and recognizing the information of “what” something is. In fact, discrete categories of objects are even associated with different regions.
*The
fusiform gyrus
The fusiform gyrus, also known as the ''lateral occipitotemporal gyrus'','' ''is part of the temporal lobe and occipital lobe in Brodmann area 37. The fusiform gyrus is located between the lingual gyrus and parahippocampal gyrus above, and the inf ...
or
Fusiform Face Area
The fusiform face area (FFA, meaning spindle-shaped face area) is a part of the human visual system (while also activated in people blind from birth) that is specialized for facial recognition. It is located in the inferior temporal cortex ( ...
(FFA) deals more with facial and body recognition rather than objects.
![Gray727 fusiform gyrus](https://upload.wikimedia.org/wikipedia/commons/7/7e/Gray727_fusiform_gyrus.png)
*The
Parahippocampal Place Area
The parahippocampal gyrus (or hippocampal gyrus') is a grey matter cortical region of the brain that surrounds the hippocampus and is part of the limbic system. The region plays an important role in memory encoding and retrieval. It has been inv ...
(PPA) helps differentiate between scenes and objects.
![Gray727 parahippocampal gyrus](https://upload.wikimedia.org/wikipedia/commons/4/4c/Gray727_parahippocampal_gyrus.png)
*The
Extrastriate Body Area The extrastriate body area (EBA) is a subpart of the extrastriate visual cortex involved in the visual perception of human body and body parts, akin in its respective domain to the fusiform face area, involved in the perception of human faces. The ...
(
EBA
Ẹ̀bà (in Nigeria) or Pinon (in Togo, Benin, and southern Ghana) is a staple food mainly eaten in the West African sub-region and other African countries. The term èbà originates from the Yoruba people of southwest Nigeria. It is a coo ...
) helps differentiate body parts from other objects.
*And the Lateral Occipital Complex (LOC) is used to determine shapes vs. scrambled stimuli.
These areas must all work together, as well as with the
hippocampus
The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
, in order to create an array of understanding of the physical world. The hippocampus is key for storing the memory of what an object is/what it looks like for future use so that it can be compared and contrasted with other objects. Correctly being able to recognize an object is highly dependent on this organized network of brain areas that process, share, and store information. In a study by Denys et al., functional magnetic resonance imaging (
FMRI
Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
) was used to compare the processing of visual shape between humans and macaques. They found, amongst other things, that there was a degree of overlap between shape and motion sensitive regions of the cortex, but that the overlap was more distinct in humans. This would suggest that the human brain is better evolved for a high level of functioning in a distinct, three-dimensional, visual world.
Clinical significance
Prosopagnosia
Prosopagnosia
Prosopagnosia (from Greek ''prósōpon'', meaning "face", and ''agnōsía'', meaning "non-knowledge"), also called face blindness, ("illChoisser had even begun tpopularizea name for the condition: face blindness.") is a cognitive disorder of fac ...
, also called face blindness, is a disorder that results in the inability to recognize or discriminate between faces. It can often be associated with other forms of recognition impairment, such as place, car, or emotional recognition. A study conducted by Gross et al. in 1969 found that certain cells were selective for the shape of a monkey hand, and they observed that as the stimulus they provided began to further resemble a monkey hand, those cells became more active. A few years later, in 1972, Gross et al. discovered that certain IT cells were selective for faces. Although it is not conclusive,
‘face-selective’ IT cortex cells are assumed to play a large role in facial recognition in monkeys.
After the extensive research into the result of damage to the IT cortex in monkeys, it is theorized that lesions in the IT gyrus in humans result in prosopagnosia. Rubens and Benson's 1971 study of a subject in life with prosopagnosia reveals that the patient is able to name common objects on visual presentation flawlessly, however she cannot recognize faces. Upon necropsy conducted by Benson et al., it was apparent that a discrete lesion in the
right fusiform gyrus, a part of the inferior temporal gyrus, was one of the main causes of the subject's symptoms.
A more in depth observation can be seen with the example of patient L.H. in the study conducted by N.L. Etcoff and colleagues in 1991. This 40-year-old man was involved in an automobile accident when he was 18, which resulted in severe brain injury. Upon recovery, L.H. was unable to recognize or discriminate between faces, or even recognize faces that were familiar to him before the accident. L.H. and other patients with prosopagnosia are often able to live relatively normal and productive lives despite their deficit. L.H. was still able to recognize common objects, subtle differences in shapes, and even age, sex, and “likeability” of faces. However, they use non-facial cues, such as height, hair color, and voice to differentiate between people. Non-invasive brain imaging revealed that L.H.’s prosopagnosia was a result of damage to the
right temporal lobe, which contains the inferior temporal gyrus.
Deficits in semantic memory
Certain disorders, such as
Alzheimer's disease
Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...
and
semantic dementia
Semantic dementia (SD), also known as semantic variant primary progressive aphasia (svPPA), is a progressive neurodegenerative disorder characterized by loss of semantic memory in both the verbal and non-verbal domains. However, the most common p ...
, are characterized by a patient's inability to integrate semantic memories, which results in patients being unable to form new memories, lacking awareness of time period, as well as lacking other important cognitive processes. Chan et al 2001 conducted a study that used volumetric magnetic resonance imaging to quantify the global and temporal lobe atrophy in semantic dementia and Alzheimer's disease. The subjects were selected and confirmed to be in the middle of the spectrum of their respective disorders clinically, and then further confirmation came from a series of neuropsychological tests given to the subjects. The study treated the inferior temporal cortex and the middle temporal cortex as one and the same, because of the, "often indistinct," border between the gyri.
The study concluded that in Alzheimer's disease, deficits in inferior temporal structures were not the main source of the disease. Rather, atrophy in the
entorhinal cortex
The entorhinal cortex (EC) is an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time.Integrating time from experience in the ...
,
amygdala
The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...
, and
hippocampus
The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
was prominent in the Alzheimer's inflicted subjects of the study. With respect to semantic dementia, the study concluded that “the middle and inferior temporal gyri
orticesmay play a key role” in semantic memory, and as a result, unfortunately, when these anterior temporal lobe structures are injured, the subject is left with semantic dementia. This information shows how, despite often being grouped in the same category, Alzheimer's disease and semantic dementia are very different diseases, and are characterized by marked differences in the subcortical structures they are associated with.
Cerebral achromatopsia
Cerebral achromatopsia
Cerebral achromatopsia is a type of color-blindness caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye's retina. It is often confused with congenital achromatopsia but underlying physiological de ...
is a medical disorder characterized by the inability to perceive color and to achieve satisfactory visual acuity in high light levels.
Congenital achromatopsia is characterized the same way, however it is genetic, while Cerebral Achromatopsia occurs as a result of damage to certain parts of the brain. One part of the brain that is particularly integral to color discrimination is the inferior temporal gyrus. A 1995 study conducted by Heywood et al. was meant to highlight the parts of the brain that are important in achromatopsia in monkeys, however, it obviously sheds light on the areas of the brain related to achromatopsia in humans. In the study, one group of monkeys (group AT) received lesions in the temporal lobe anterior to V4 and the other group (group MOT) received lesions to the occipito-temporal area that corresponds in cranial location to the lesion that produces cerebral achromatopsia in humans. The study concluded that group MOT had no impairment of their color vision while the subjects in group AT all had severe impairments to their color vision, consistent with humans diagnosed with cerebral achromatopsia.
This study shows that temporal lobe areas anterior to V4, which includes the inferior temporal gyrus, play a large role in patients with Cerebral Achromatopsia.
Additional images
File:Inferior temporal gyrus animation small.gif, Position of inferior temporal gyrus (shown in red).
File:Gehirn, basal - beschriftet lat.svg, Basal view of a human brain
File:Gehirn, lateral - Hauptgyri beschriftet.svg, Lateral view of a human brain, main gyri labeled.
File:Slide2HAN.JPG, Cerebrum. Lateral view. Deep dissection. Inferior temporal gyrus labeled at bottom center.
File:Inferior Temporal - DK ATLAS.png, Inferior temporal gyrus, right hemisphere.
File:Inferior temporal gyrus coronal sections.gif, Inferior temporal gyrus highlighted in green on coronal T1 MRI images
File:Inferior temporal gyrus sagittal sections.gif, Inferior temporal gyrus highlighted in green on sagittal T1 MRI images
File:Inferior temporal gyrus transversal sections.gif, Inferior temporal gyrus highlighted in green on transversal T1 MRI images
See also
*
Cognitive neuroscience of visual object recognition
Visual object recognition refers to the ability to identify the objects in view based on visual input. One important signature of visual object recognition is "object invariance", or the ability to identify objects across changes in the detailed c ...
*
Face perception
Facial perception is an individual's understanding and interpretation of the face. Here, perception implies the presence of consciousness and hence excludes automated facial recognition systems. Although facial recognition is found in other spec ...
*
Neural processing for individual categories of objects Discrete categories of objects such as faces, body parts, tools, animals and buildings have been associated with preferential activation in specialised areas of the cerebral cortex, leading to the suggestion that they may be produced separately in d ...
*
Visual cortex
The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...
References
External links
Image at University of Utah
{{Authority control
Gyri
Temporal lobe