A study conducted in 2012-2014 revealed that the primary sensory cortices and the amygdala of participants with Autism Spectrum Disorder exhibited stronger activation than the primary sensory cortices and the amygdala of neurotypical participants. The stronger activation in primary sensory cortices and the amygdala in the participants with ASD were strongly correlated with sensory over-responsivity symptoms. The researchers also found differences in the neural habituation to stimuli in sensory cortices and the amygdala between the participants with ASD that have sensory over-responsivity and the participants with ASD that do not have sensory over-responsivity. The participants with ASD and sensory over-responsivity exhibited decreased neural habituation to stimuli in their sensory cortices and their amygdala. The participants with ASD without sensory over-responsivity exhibited amygdala downregulation, with negative connectivity between the amygdala and orbitofrontal cortex.

Neurobiology of sensory symptoms in ASD (research)

Since more than half of children with Autism Spectrum Disorder (ASD) display sensory over-responsivity, are there differences in brain response, habituation, and connectivity during exposure to sensory stimuli between children with ASD and sensory over-responsivity, compared to neurotypical children?

Lawrence University

The DSM-5 criteria for children with ASD includes deficits in sensory processing, specifically sensory modulation. Any sensory modality may be affected but some evidence suggests that individuals with ASD have a greater frequency of sensory deficits in the domains of taste and smell, as well as tactile sensitivity. 

- neurobiology of sensory symptoms in ASD

Sensory Processing Deficits in Autism Spectrum Disorder

The amygdala is a key brain structure that plays a central role in processing and relaying emotional information, making it a major focus of research into the biological basis of emotions like fear and anxiety. It is composed of various subnuclei and has a crucial role in memory, influencing how memories are stored—a process affected by stress hormones—and is involved in memory consolidation, the transfer of new learning into long-term memory. This is facilitated by enabling a deeper level of memory encoding for emotionally arousing events.

Amygdala

The primary somatosensory cortex (S1) is located in both hemispheres and lies in the postcentral gyrus of the parietal cortex, just behind the central sulcus dividing the parietal lobe from the frontal lobe. Each S1 receives touch information from the opposite side of the body. 
- Topographic Mapping
- Plasticity of the Sensory Cortex

Primary Sensory Cortex

Green, S. A., Hernandez, L., Tottenham, N., Krasileva, K., Bookheimer, S. Y., & Dapretto, M. (2015). Neurobiology of Sensory Overresponsivity in Youth With Autism Spectrum Disorders. JAMA Psychiatry, 72(8), 778. https://doi.org/10.1001/jamapsychiatry.2015.0737

Neurobiology of sensory issues in ASD reference

While children with ASD may also have deficits in sensory processing, the behavioral profiles of sensory processing in children with ASD and children with SPD may differ. 

Differentiating between Sensory Processing Disorder and Austism Spectrum Disorder

Neurobiology of sensory symptoms in ASD (research question)

Treatment (and possible treatment) for Sensory Integration Dysfunction/Sensory Processing Disorder

The neurotransmitter GABA is heavily involved in sensory integration, and reduced GABA levels have been observed in children with ASD compared to children without ASD

This could be a key reason for sensory issues in ASD, with sensory processing issues having a prevalence rate of 90% in people with ASD

Role of GABA Neurotransmitter in Sensory Processing and ASD

Strategic use of deep pressure (defined as the sensation provided when an individual is hugged, squeezed, stroked, or held), often used by occupational therapists when working with patients with ASD

Deep Pressure Therapy

Mindfulness-Based Stress Reduction (MBSR) interventions have been shown to increase connectivity between the amygdala and the ventromedial prefrontal cortex (VMPFC). This could, in turn, increase abilities to regulate emotions.

Neurological Effects Resulting From Mindfulness-Based Stress Reduction: Increased connection between the amygdala and the ventromedial prefrontal cortex (VMPFC)

The amygdala is a section of the brain that processes fearful stimuli. Patients with anxiety disorders exhibit stronger amygdala responses than patients without anxiety disorders. Studies suggest that mindfulness interventions can reduce the amygdala response in patients with anxiety disorders.

Mindfulness Effects on the Amygdala and Anxiety

Due to its role in processing emotional information, the amygdala is heavily involved in memory consolidation, which is the process of transferring newly learned information into long-term memory. It facilitates the encoding of memories at a much deeper level when the event is emotionally arousing.

Amygdala's Role in Memory Consolidation

Josselyn's 2010 experiment with rats illustrates the amygdala's role in memory storage. Using Pavlovian conditioning, rats were taught to associate a neutral tone with a foot shock, which produced a fear memory causing them to freeze defensively upon hearing the tone. However, when researchers induced cell death in the neurons of the lateral amygdala, the conditioned fear memory faded and became extinct, demonstrating that this region is essential for retaining fear-based memories.

Example of Amygdala's Role in Fear Memory: Josselyn's Rat Experiment

The amygdala is composed of various subnuclei, two of which are the basolateral complex and the central nucleus.

Subnuclei of the Amygdala

A study by Raineki et al. (2012) investigated the impact of negative early life experiences on rat pups. Pups were subjected to abusive conditions between postnatal days 8 and 12, which included either the mother having insufficient bedding material to build a proper nest or the pups undergoing fear conditioning (pairing an odor with a shock) without their mother present. Compared to a control group raised in normal conditions, the abused pups displayed more depressive-like behaviors during adolescence. These behavioral changes were correlated with heightened activation in the amygdala, suggesting that early life trauma can alter amygdala function and lead to behaviors that model human mood disorders.

Early Life Abuse in Rats Alters Amygdala Function and Induces Depressive-Like Behaviors

Human studies indicate a significant link between the amygdala and psychological conditions such as mood and anxiety disorders. Evidence shows that adolescents who are either diagnosed with or at high risk for these disorders often exhibit alterations in both the structure and function of their amygdala.

Amygdala's Role in Human Mood and Anxiety Disorders

Given the following scenario, identify the brain structure most responsible for the difference in memory recall between the two individuals and explain the mechanism behind this difference.

Emotional Memory Formation

Given the following scenario, identify the brain structure most responsible for the described emotional and memory-related responses and explain your reasoning.

Emotional Memory and Brain Function

Henry Molaison (H.M.) is one of psychology's most famous case studies. In 1953, surgeons removed large sections of his hippocampus to treat severe epilepsy. While the surgery successfully stopped his seizures without affecting his IQ or personality, it left him with anterograde amnesia. His short-term memory remained intact, but he permanently lost the ability to transfer new information into long-term memory—a process known as consolidation. This case was crucial for memory research because it demonstrated a clear dissociation between short-term and long-term memory and highlighted the temporal lobes' essential role in memory consolidation.

Case of Henry Molaison (H.M.)

The lateral amygdala is the specific area of the brain that is responsible for fear memories.

Lateral Amygdala

The cells in each primary sensory cortex is arranged according to the plan of the body surface. Each region is a map of the body in which the relative areas devoted to body regions reflect the density of body innervation. Furthermore, parts of the body where we are especially sensitive to touch (like our hands and fingers) send information to a larger area of S1 than do less sensitive body regions (like our shoulder).
The attached picture shows the two homunculi (little men), which represent how we would appear if our body proportions matched cortical representations. As you can see, the hands and face far outweigh other body parts in representation due to innervation. 

Topographic Mapping

Plasticity of the sensory cortex refers to a characteristic of the cortex, that the cortical maps can change with experience. This was demonstrated in an experiment by Merzenich and Jenkins (1993), where they surgically removed the middle finger of the monkey, then found later that the region of cortex that responded to each remaining, adjacent finger expanded.

Plasticity of the Sensory Cortex

An Elite Cafemedia. (n.d.). Primary Somatosensory Cortex (In Blue). Know Your Brain: Primary Somatosensory Cortex. https://www.neuroscientificallychallenged.com/blog/know-your-brain-primary-somatosensory-cortex. 

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