Sensory Gating in Autism, Particularly Asperger's

Sensory gating is an issue in autism, schizophrenia and ADHD.   It is the neurological process of filtering out redundant or unnecessary stimuli in the brain; like the child who sits in his classroom and gets bothered by the noise of the clock on the wall.  He is unable to filter out and ignore this sound. He becomes preoccupied by the sound and cannot concentrate on his work.

There are also sometimes advantages to not filtering out environmental stimuli, because you would have more situational awareness and notice things that others miss.

An example of sensory gating is the fact that young children are not waken by smoke detectors that have high pitched siren, but are waken by a recorded human voice telling them there is a fire and to wake up.

There may be times when sensory overload in autism is not a case of too much volume from each of the senses, but rather too many inputs being processed by the brain, instead of some just being ignored.  It is more a case of information overload.

Note that this blog has already covered hypokalemic sensory overload in some depth, which is treatable.

Much is known about sensory gating because it has long been known to be a problem in schizophrenia.

An EEG (Electroencephalography) test measures your brain waves / neural oscillations. Many people with autism have EEGs, but mainly those in which epilepsy is a consideration.

In the world of the EEG, the P50 is an event occurring approximately 50 millisecond after the presentation of an auditory click.  The P50 response is used to measure sensory gating, or the reduced neurophysiological response to redundant stimuli.

Abnormal P50 suppression is a biomarker of schizophrenia, but is present in other disorders, including Asperger’s, post-traumatic stress disorder (PTSD) and traumatic brain injury (TBI).

In more severe autism abnormal P50 suppression was found not to be present in one study.  This might be because cognition and the senses are dimmed by the excitatory-inhibitory imbalance.

More broadly, sensory gating is seen as an issue in wider autism and ADHD.

Correcting P50 gating

It is known that α7 nicotinic acetylcholine receptor (α7 nAChR) agonists can correct the impaired P50 gating. It is also known that people with schizophrenia have less expression of this receptor in their brains than typical people.

One short term such agonist is the nicotine released from smoking.  This likely contributes to why people with schizophrenia can be heavy smokers.  The effect is thought to last for about 30 minutes.

Clinical trials using Tropisetron, a drug that is a α7 nAChR agonist and used off-label to treat fibromyalgia, have shown that it can correct defective P50 gating and improve cognitive function in schizophrenia.

An alternative α7 nAChR agonist that is widely available is varenicline, a drug approved to help people stop smoking.

So you might expect varenicline to improve P50 gating and improve cognition. You might also expect it to help people with fibromyalgia and indeed some other people with chronic inflammation, as shown by elevated inflammatory cytokines.

You may recall that the α7 nAChR is the key to stimulating the vagus nerve and this should be beneficial to many people with inflammatory conditions (from arthritis to fibromyalgia).

Brief Report: Initial Trial of Alpha7-Nicotinic Receptor Stimulation in Two Adult Patients with Autism Spectrum Disorder

Abnormalities in CHRNA7, the alpha7-nicotinic receptor gene, have been reported in autism spectrum disorder. These genetic abnormalities potentially decrease the receptor’s expression and diminish its functional role. This double-blind, placebo-controlled crossover study in two adult patients investigated whether an investigational receptor-specific partial agonist drug would increase the inhibitory functions of the gene and thereby increase patients’ attention. An electrophysiological biomarker, P50 inhibition, verified the intended neurobiological effect of the agonist, and neuropsychological testing verified a primary cognitive effect. Both patients perceived increased attention in their self-ratings. Alpha7-nicotinic receptor agonists, currently the target of drug development in schizophrenia and Alzheimer Disease, may also have positive clinical effects in autism spectrum disorder.

α7-nicotinic acetylcholine receptor agonists for cognitive enhancement in schizophrenia

A role for H3 and HI histamine receptors

It has also been suggested that histamine plays a role in sensory gating via the H1 and H3 receptors.

It had also been thought H3 receptors could be targeted to improve cognition in schizophrenia, but that research really did not go anywhere.

Meclizine enhancement of sensorimotor gating in healthy male subjects with high startle responses and low prepulse inhibition.

Histamine H₁ receptor systems have been shown in animal studies to have important roles in the reversal of sensorimotor gating deficits, as measured by prepulse inhibition (PPI). H₁-antagonist treatment attenuates the PPI impairments caused by either blockade of NMDA glutamate receptors or facilitation of dopamine transmission. The current experiment brought the investigation of H₁ effects on sensorimotor gating to human studies. The effects of the histamine H₁ antagonist meclizine on the startle response and PPI were investigated in healthy male subjects with high baseline startle responses and low PPI levels. Meclizine was administered to participants (n=24) using a within-subjects design with each participant receiving 0, 12.5, and 25 mg of meclizine in a counterbalanced order. Startle response, PPI, heart rate response, galvanic skin response, and changes in self-report ratings of alertness levels and affective states (arousal and valence) were assessed. When compared with the control (placebo) condition, the two doses of meclizine analyzed (12.5 and 25 mg) produced significant increases in PPI without affecting the magnitude of the startle response or other physiological variables. Meclizine also caused a significant increase in overall self-reported arousal levels, which was not correlated with the observed increase in PPI. These results are in agreement with previous reports in the animal literature and suggest that H₁ antagonists may have beneficial effects in the treatment of subjects with compromised sensorimotor gating and enhanced motor responses to sensory stimuli.

Histamine and acetylcholine receptor involvement in sensorimotor gating: an autoradiography study

The aim of this study was to investigate an established rat model of decreased PPI induced by administration of the NMDA antagonist, dizocilpine and the reversal of this PPI impairment by the histaminergic H1-antagonist, pyrilamine. H1-antagonism is a potential mechanism of the therapeutic effects of the atypical antipsychotic, clozapine, which improves PPI following dizocilpine administration in rats as well as in patients with schizophrenia. In the present study we show that chronic pyrilamine administration prevents the PPI impairment induced by chronic dizocilpine administration, an effect that is correlated with a reduction in ligand-binding potential of H1 receptors in the anterior cingulate and an increase in nicotinic receptor α7 subunit binding in the insular cortex. In light of the functional anatomical connectivity of the anterior cingulate and insular cortex, both of which interact extensively with the core PPI network, our findings support the inclusion of both cortical areas in an expanded network capable of regulating sensorimotor gating.

Histamine H3 Receptor Regulates Sensorimotor Gating and Dopaminergic Signaling in the Striatum.

The brain histamine system has been implicated in regulation of sensorimotor gating deficits and in Gilles de la Tourette syndrome. Histamine also regulates alcohol reward and consumption via H3 receptor (H3R), possibly through an interaction with the brain dopaminergic system. Here, we identified the histaminergic mechanism of sensorimotor gating and the role of histamine H3R in the regulation of dopaminergic signaling. We found that H3R knockout mice displayed impaired prepulse inhibition (PPI), indicating deficiency in sensorimotor gating. Histamine H1 receptor knockout and histidine decarboxylase knockout mice had similar PPI as their controls. Dopaminergic drugs increased PPI of H3R knockout mice to the same level as in control mice, suggesting that changes in dopamine receptors might underlie deficient PPI response when H3R is lacking. Striatal dopamine D1 receptor mRNA level was lower, and D1 and D2 receptor-mediated activation of extracellular signal-regulated kinase 1/2 was absent in the striatum of H3R knockout mice, suggesting that H3R is essential for the dopamine receptor-mediated signaling. In conclusion, these findings demonstrate that H3R is an important regulator of sensorimotor gating, and the lack of H3R significantly modifies striatal dopaminergic signaling. These data support the usefulness of H3R ligands in neuropsychiatric disorders with preattentional deficits and disturbances in dopaminergic signaling.

Conclusion

Other than nicotine, varenicline would seem a good potential therapy for sensory gating.  There are α7-nicotinic acetylcholine receptor agonists in development.

There are many H1 histamine antagonists.  Histamine release in the brain triggers secondary release of excitatory neurotransmitters such as glutamate and acetylcholine via stimulation of H₁ receptors. Centrally acting H1 antihistamines are sedating.

H3 antagonists have stimulant and nootropic effects. Betahistine is an approved drug in this class, there are many research drugs.

The role of histamine dysfunction in sensory and cognitive deficits in schizophrenia

The aim of this study is to investigate the role of the neurotransmitter histamine in sensory and cognitive deficits as they often occur in schizophrenia patients (e.g. hearing voices, planning and memory problems). The ideal location to conduct the study and to obtain a unique learning experience is at the Institute of Psychiatry, London, United Kingdom, where staff comprises of leading experts in the field of schizophrenia and Magnetic Resonance Imaging of pharmacological effects. Current pharmacological treatment of psychotic symptoms including sensory and cognitive deficits remains partially unsuccessful due to side effects and treatment resistance. The neurotransmitter histamine seems to be a very promising target for new treatments. It has been found that histamine neurotransmission is altered in brains of schizophrenics, which may contribute to both the hallucinatory and cognitive symptoms. However, this specific role of histamine has not been investigated before. I will assess the effects of increased histaminergic activity, by administration of betahistine to healthy volunteers, on performance (sensory gating, executive functioning or planning and memory) and associated brain activity using fMRI. Altered performance and brain activity would support the importance of histamine in schizophrenia and would provide a research model and target for new treatments.

Epsom salts, Autism and Hypokalemic Sensory Overload

Early on in this blog I wrote about a supposedly rare condition, where somebody suffers from sensory overload, usually from sound, but it could be light or even smell.  That condition has fancy sounding name, Hypokalemic Sensory Overload.  The cure is very simple, just to give oral potassium and within 20 minutes there is a full recovery.  Here is one research study.

 

I felt it odd that nobody had compared this to sensory overload in autism.  I did my own experiment at home and found to my surprise that sensory overload in autism could also be treated with oral potassium.

In the last few weeks I received two very thoughtful comments on this blog, from adult sufferers who have found the same remedy as I have.  So at least I am no longer in a minority of one.

The interesting thing about potassium in the human body is that it relies on another electrolyte, magnesium.  Without sufficient magnesium, the body cannot maintain an adequate level of potassium.  This is why supplements normally contain both potassium and magnesium.  A problem with both potassium and magnesium is that they very easily upset the stomach, indeed some laxatives are based on magnesium.

Epsom salts

I have noted that the long list of autism interventions used in the US, frequently includes having a bath in Epsom salts.  Epsom salts are named after a town near London, England, from which they were originally mined.  Epsom salts are just magnesium sulphate (MgSO4).

In the “biomedical” community it is proposed that magnesium does great things for autism and/or sulphur does.

The sulphur part at least has a scientific explanation.  It was long ago shown that there is an apparent abnormality in the sulphur metabolism in autism. 

In effect there is greater loss than normal of sulphur in the urine, resulting in lower plasma levels than in typical people.

So people are dipping their kids in Epsom salts on that basis that either the magnesium or the sulphur will do some good, not sure of which.

Interestingly, on the web, I found one mother writing about the Epsom salts baths she gives her child; she says she know when it is time for another one, where her child starts to cover her ears (sound sensory overload).

Trans-dermal Magnesium

Since magnesium supplements are in-effect laxatives, other ways have been sought to administer this electrolyte.  There are several transdermal creams and sprays that do indeed seem to work, but they can irritate the skin.  Interestingly, also on the web, some autistic adults talk about using such supplements and benefiting. 
 

Making the Connection

Well I hope this is all obvious to you, at least one of the things that is going on is an ion channel disease, the result of which is sensory overload in autism.  By chance, some people have stumbled upon magnesium supplementation as a therapy.  The extra magnesium is making whatever potassium there is in that person’s diet more effective, and hence reducing their symptoms.  Since the condition is actually Hypokalemic Sensory Overload, they would do even better to add some extra potassium as well.

The sulphur part may, or may not be, a red herring.  Sadly there are many of them in autism.

Conclusion

I have completed this part of my autism investigation.  If you want to treat autistic sensory overload, that seems to affect almost all people with ASD and most with ADHD, the options are:-

1.     Reduce the body’s daily loss of potassium and magnesium, with a potassium sparing diuretic, like Spironolactone

2.     Increase consumption of potassium and magnesium in diet.  Bananas, oranges and kiwis are rich in potassium, for example.

3.     Use small doses of oral potassium and magnesium supplements throughout the day

4.     Use expensive transdermal magnesium treatments.  Nobody seems to make a potassium version.

5.     Take a soak in the bath with an added cup of Epsom salts.

There should be a second reason to try option (1).  For entirely unrelated reasons, this drug is proposed to help in autism due to its secondary anti-inflammatory and hormonal effects.
Spironolactone might be a desirable immunologic and hormonal intervention in autism spectrum disorders

 I have to say that, having done my field research, I will be sticking with (2), (3) and the occasional (5)