Deficits in various forms of musical processing can result in a diverse number of musical
disorders that can impede the development and even the execution of numerous well
established musical skills. Such deficits in musical processing can occur as a result of music_brain.jpg
traumatic injuries to the brain or they can also be congenitally acquired[1] . In recent decades,
there has been a sudden research interest in musical disorders due to the significant impact it
has on various brain regions and underlying cognitive processes. Better comprehension of
the impairments presented by these disorders can further help in the understanding of the
effects of musical processing on the normal brain[2] . The most interesting aspect of musical
disorders is that though specific musical abilities are severely impaired, other cognitive
systems that require the same perceptual processes remain relatively intact. Musical
disorders such as congenital amusia and musical hallucinations have been widely researched
within the field of neuroscience and these two disorders also have a common within
the population. Musicogenic epilepsy on the other hand, is a very rare form of epilepsy that can
be induced by a wide range of musical triggers.




Musicogenic Epilepsy

Musicogenic Epilepsy (ME) is a rare form of reflexive epilepsy in which seizures can be
induced by a vast array of musical triggers.As a rare musical disorder that has a very low
prevalence in the general population; comprehension of the underlying cognitive
mechanisms is dependent on detailed examination of individual case studies
as the disorder greatly varies in its severity and complexity amongst individuals affected
with ME. The incidence of this disorder does not differentially vary amongst the sexes and
it has been found to commence with the greatest rate during a patient’s adult years. A very
unique aspect of ME, is that there has to be a delay of approximately 5 minutes between the
occurrence of the musical stimulus and the onset of the seizures[3] . The prominent form of
seizure activity that occurs in individuals with ME is either complex partial seizures or grand
mal seizures and this typically tends to arise specifically from the right temporal lobe. However
being a very complex disorder, that is quite heterogeneous in nature, there have been a few
individual cases of ME that have demonstrated epileptic seizures arising from the left
temporal lobe as well[4] .




Video: Dr.Ashesh Mehta a leading researcher in Musicogenic Epilepsy discusses this very rare musical disorder




Musicogenic Triggers

Musicogenic triggers vary great amongst individuals affected with ME. The onset of music induced seizures, primarily stem from instrumental music in comparison to vocal music. Musical triggers are specific to an individual and include stimuli such as church bells, hissing of a kettle, instrumental specificity, vocal specificity, different genres of music, and even specific songs sung by specific individuals. The intensity of the musical stimuli can also vary from being very loud to very soft in terms of the musical pitch. Though seizures can be induced in individuals with ME from single tones, this only accounts for 4% of the patient population. Musical processing occurs at three different levels: sensory level (lowest), emotional level, and anesthetic appreciation level (highest)[5] . The low prevalence of single tone induced seizures suggests ME requires a high level of musical processing. Musical triggers specific to an individual often include an emotional content which further indicates a higher level of cognitive processing necessary for the onset of musicogenic seizures. Though musical triggers vary amongst the patient population, the most intriguing triggers that result in the successful onset of seizures tend to be emotional ones that require a higher level of musical processing.


Associative and Affective Seizures vs. Simple Sound Seizures

Individuals, who are affected with ME, can be separated into having one of two types of seizures; associative and affective seizures or simple sound seizures. Simple sound seizures consist of a small group of individuals in which seizures are initiated after hearing a simple sound such as a single tone, church bell, etc. Associative and affective seizures tends to affect a larger proportion of individuals with ME indicating that music-induced seizures requires an elevated level of cognitive processing incorporating multiple brain regions such as the primary auditory cortex and association cortex in the temporal lobe. Recent research into musicogenic epilepsy has determined that the onset of music-induced seizures is brought on by an associative learning process that operates through the hippocampus[6] . After the musical stimuli is processed within the primary auditory cortex and the association cortex, it then undergoes further processing in the hippocampus and the amygdala. Such processing will allow the individual to acquire a better emotionally induced memory for the specific stimuli. With the onset of a seizure to the particular stimuli, a firm associative connection is made between the seizure and the musical stimuli; this will increase the likelihood of a seizure being initiated in the hippocampus the next time the same musical trigger is perceived. The associative connections to other areas of the brain from the hippocampus will allow the seizure activity to expand across various regions of the brain.


Treatment Options for ME

A number of treatment options have been suggested for ME such as avoidance of stimulus, surgical procedures and behavioural conditioning procedures.


Avoidance of Stimulus

One of the easiest and quickest methods to relieve oneself from a possible onset of a music-induced seizure is to do one’s best to completely avoid the musical trigger that is causing the onset of the seizure; this is often referred to as the avoidance of stimulus. A disadvantage of such an approach is that individuals will develop a form of phobia towards the particular musical stimulus one is trying to avoid[7] .


Epilepsie1.jpg
Figure 1: Surgical Procedure on an Epileptic Brain.
Surgical Procedures


Surgical removal of the right temporal lobe (Figure 1) is a common procedure used to relieve an individual from the devastating seizures experienced from perceiving specific musical stimulus. While conducting such procedures, physicians have to cautiously spare
the hippocampus because if it is lesioned accidently, this will cause further cognitive damage[8] .This is often a very successful procedure for individuals suffering from
musicogenic epilepsy as individuals often report a drastic reduction in
music-induced seizures post-surgically.

Behavioural Conditioning Procedures

A non-invasive procedure for individuals with musicogenic epilepsy is a behavioural therapy technique known as sensory extinction. In this form of therapy, individuals are first exposed to music similar to the seizure inducing musical stimuli prior to exposing the individual to the actual musical trigger. By exposing the individual to similar music, the neurons that normally respond to the musical trigger become less conditioned, and eventually when the actual musical trigger is presented, the individual experiences sensory extinction. Unfortunately with this form of therapy, individuals often experience a high rate of spontaneous recovery, and further therapy sessions are required to induce sensory extinction once again.


Congenital Amusia

Congenital amusia is a more prevalent neurodevelopmental musical disorder that occurs in approximately 4% of the population[9] . Individuals with congenital amusia are born with deficits in the ability to perceive and produce melody. These individuals have intact hearing abilities and have been exposed to music, so it is not a lack of exposure or hearing disability that is the underlying cause for this disorder[10] . This condition is not the same as acquired amusia which refers to the inability to efficiently produce and perceive music resulting from damage to the brain post-natal. One of the primary musical deficits that can be observed in these individuals is pitch perception and they often spend a long duration on tasks involving pitch. These individuals fail to detect changes in pitch, holding pitch information in short term memory and noticing changes in vocal pitches as well10. These individuals will try to exist with their musical disabilities by either trying to avoid all possible musical stimuli or by taking additional musical therapy to help them learn how to handle situations in which they encounter musical stimuli.


Neural Correlates

Recent research in congenital amusia has made an interesting discovery with
regards to the underlying neural correlates of congenital amusia. Previous
studies have shown that an overall neurological abnormality was not observed
when comparing amusic brains with normal control brains. However, there
cortical_thickk.png
Figure 2: Differences in Cortical Thickness between Controls and Amusic. Adapted from Hyde et al. (2007)

appears to be a significant difference in the amount of grey and white matter
found in right inferior frontal gyrus (IFG) and in the auditory cortex among
individuals with congenital amusia. Specifically, there is a large reduction in
the amount of white matter in the right IFG in comparison to normal control
brains, and on the other hand, an increase in gray matter has also been noted in the
right IFG of amusic brains[11] (Figure 2) . The right inferior cortex also forms connections to the right auditory cortex and this pathway is significantly impoverished in individuals with congenital amusia due to the decrease in white matter along with a substantial increase in gray matter that resulted from the abnormal neural migration to these areas during development[12] . This further results in a thicker cortex in both the right inferior gyrus and right auditory cortex.These areas have been implicated to be important brain regions for pitch perception in normal controls, and lesions to such areas in normal individuals result in similar pitch perception deficits as those observed in individuals with congenital amusia, further providing evidence that the immature development in these areas is the underlying neural mechanism for congenital amusia.


Strong Genetic Loci for Pitch Deficits

Congential amusia appears to have a very strong genetic connection with regards to the unfortunate pitch deficits experienced by individuals as a result of this disorder. In order to test the genetic heritability of congenital amusia, researchers have conducted genetic analysis on congenital amusic families and control families. In these studies, though no specific gene has been identified as the primary cause of congenital amusia, researchers found that 39% of first-degree relatives in amusic families also had congenital amusia in comparison to only 3% in control families12. Twin studies for congenital amusia also provided evidence that monozygotic twins had a higher genetic component for this disorder than dizygotic twins. Rather than a single gene being identified, researchers have suggested that there are multiple genes interacting with one another as well as the environment in order to produce the deficits experienced in individuals with congenital amusia13 (Figure 3). Interestingly, it has also been determined that enriching the musical environment will decrease the severe deficits experienced in these individuals, suggesting that there is a robust interaction between the genes and the environment in determining the various phenotypes of individuals affected with congenital amusia[13] .

rightgencon.png
Figure 3: Interaction of Multiple Genes to Elicit Various Pitch Deficits. Adapted from Peretz I (2008)

Pitch Processing Deficits in Tonal Languages

Congenial amusia is primarily known as a musical disorder that involves deficits in musical processing specifically with regards to pitch perception. Studies investigating the relationship between language processing and musical processing determined that deficits in pitch perception is not specific to musical processing but can also broaden its effect into pitch processing deficits in tonal languages[14] . Amusic individuals who could not discriminate between two different musical tones could also not discriminate between two different lexical tones in tonal languages as well. This provides compelling evidence that congenital amusia though once thought to be specific to musical deficits, can also cause deficits in speech as well. Although individuals with congenital amusia suffer from the inability to discriminate between two different lexical tones in tonal languages, they demonstrate no difficulties in the production of tonal languages12.



The Montreal Battery of Evaluation of Amusia as a Diagnostic Tool (MBEA)

The Montreal Battery of Evaluation of Amusia is a very efficient diagnostic tool
used to assess the musical deficits in individuals with congenital amusia and it is
also used as a therapeutic tool to improve the deficits experienced by this musical
nn0707-810-F1.gif
Figure 4: Contour Violation Task from MBEA. Adapted from Janata P (2007)

disorder. MBEA consists of 6 tests assessing different aspects of music such as
contour, interval, scale, rhythm, meter, and memory1 (Figure 4). This battery is conducted
all at once within one episode lasting about an hour and a half. The MBEA is
a very sensitive, valid and reliable tool that can be used to detect the
severity of musical deficits in congenitally amusic individuals. The limitation of
this diagnostic tool is that it is specific to individuals from Western countries, and
cannot be used on individuals who have severe cognitive deficits such as those with
Alzheimer’s disease or William Syndrome1.



Musical Hallucinations (MHs)

Musical hallucinations (MHs) are a particular form of auditory hallucinations in which music is perceived in the absence of an actual external musical stimulus[15] . This is very heterogeneous musical disorder that varies in severity amongst the affected population. MH is preferentially prevalent in elderly females who have some form of ear disease or acquired deafness primarily on the left side[16] . Individuals who experience MH, are well aware of the hallucinatory component of their particular perception, thus individuals are quite conscious of their hallucinations. Apart from acquired deafness, a number of other factors have been implicated in contributing to the underlying cause of MH. Neurological deficits attributing to this disorder include focal lesions to the temporary cortex, and atrophy to the brain. MHs have been implicated as a symptom in a number of psychiatric disorders such as depression, schizophrenia, and obsessive-compulsive disorder[17] . MH can be triggered in individuals with epilepsy and can also be triggered in individuals who are suffering from some form of intoxication. MH appears to have multiple underlying mechanisms that can result in manifestations that vary in severity.


Neural Correlates of MH

The auditory cortex plays a significant role in the production of MHs. MHs represent abnormal brain activities in the auditory cortex, particularly deficits in the left lobe of the temporal cortex that is usually active in the perception of music in normal controls. Rather MHs induce an increase activation of the right superior temporal gyrus. When the superior temporal gyrus is stimulated in normal controls, production of MHs can be observed15. SPECT studies by Kasai et al., (1999) has shown that there is increased cerebral blood flow to the right superior temporal gyrus, when individuals are experiencing MHs, indicating that there is increased neural activity in this brain region in comparison to when no MH is being experienced[18] . A number of other researchers have also conducted SPECT studies to further determine other abnormal brain activations associated with MHs. It has been established with SPECT studies in individual cases that MHs generate hyperactivation in subcortical regions such as the thalamus and the basal ganglia as well[19] .


spatiotemporal_activation_during_mh.png
Figure 5: SPECT Imaging during Musical Hallucinations. Adapted from Kasai et al. (1999)

Songs vs. Melodies

The content of musical hallucinations drastically varies amongst the affected population. Most individuals report experiences of songs that are personally familiar to them from their childhood. The songs can vary in genre from classical to rock, and it can also vary from being instrumental to vocal tunes17. Using imaging studies, researchers have found different brain regions that are activated by different types of MHs. MHs that consists of songs include bilateral activation of the temporal lobes where as melodies induce the unilateral activation of the right temporal lobe[20] . Interestingly even though the musical stimulus is being perceived by the individual in the absence of the actual external stimulus, the brain can still perceptually differentiate between the quality of the stimulus even in its external absence.



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