HISTORICAL NOTE AND NOMENCLATURE

Reflex seizures of different types have been known for centuries. Recognition of those induced by flashing light predates the invention of the EEG and of the stroboscope and reaches to classical antiquity. The seizures induced by stimuli in sensitive patients are not different from spontaneous seizures in other subjects and thus reflex seizures are often classified according to the stimuli that trigger them rather than by the type of seizure that is triggered. Some earlier classifications and the publications on which they were based described “simple” and “complex” reflex epilepsies. The complex reflex epilepsies were characterized by seizures triggered by relatively elaborate stimuli whose specific pattern is the determining factor in seizure evocation. The seizures are precipitated by integration of higher cortical function and may be evoked by anticipation of the stimulus. Latency from stimulus onset to the clinical or EEG event is typically longer than in “simple” reflex epilepsies. These properties, enunciated in the 1985 proposal for classification of epilepsies (Commission on Classification and Terminology of the International League Against Epilepsy 1985), were first systematically described in the pioneering work of Forster (Forster 1972). In a later classification proposal (Commission on Classification and Terminology of the International League Against Epilepsy 1989), some varieties were not accepted as epileptic syndromes, partly because of the occurrence of spontaneous seizures in the same patients; they were described as “epilepsies characterized by specific modes of seizure precipitation”. The current proposal (Engel, 2001) upon which this article is based, defines reflex epilepsy syndromes as those “… in which all epileptic seizures are precipitated by sensory stimuli. Reflex seizures that occur in focal and generalized epilepsy syndromes that are also associated with spontaneous seizures, are listed as seizure types”. Thus, few reflex epilepsy syndromes are recognized, and are described in chapters AA-BB. The classification proposal also includes a list of precipitating stimuli for reflex seizures, discussed in this article. These are:

• Visual stimuli
• Flickering light - color to be specified when possible
• Patterns
• Other visual stimuli
• Thinking
• Praxis
• Reading
• Somatosensory
• Proprioceptive
• Eating
• Music
• Hot water
• Startle

It is important to note that the seizures which are triggered by these stimuli in epileptic disorders that are not Epilepsy Syndromes in the recent classification proposal do not differ from those triggered by the same stimulus in recognized Epilepsy Syndromes. For example, seizures triggered by flashing light in “Pure” photosensitive epilepsy (See Chapter __) are indistinguishable from the photosensitive seizures that occur in some patients with Juvenile Myoclonic Epilepsy (JME, Herpin-Janz syndrome). It should also be emphasized that when reflex seizures occur with focal epilepsy, reportedly normal imaging studies may be misleading; subtle cortical dysplastic lesions may be missed unless special MRI techniques are used or may be found only in a surgical pathology specimen (for an example see Martinez et al., 2000).

MECHANISMS

Two types of animal model of reflex seizures are: the study of irritative cortical lesions and their activation by specific stimuli, and the study of naturally occurring reflex epilepsies or seizures induced by specific sensory stimulation in genetically predisposed animals. The first approach has been used since 1929, when Clementi induced convulsions with intermittent photic stimulation after applying strychnine to the visual cortex of dogs to make it hyperexcitable. Photic-induced seizures could be triggered even if only a limited brain area were treated with strychnine as long as it was applied to both occipital cortices. Strychninization of other sensory cortices also produced focal irritative lesions that could be induced to produce seizures with the appropriate afferent stimulus, indicating a more general mechanism that does not depend on some specific property of the visual cortex. The second experimental approach, the study of naturally occurring or induced reflex seizures in genetically susceptible animals, has been pursued in photosensitive epileptic chickens, rodents susceptible to sound-induced convulsions, the E1 mouse sensitive to vestibular stimulation, and the Mongolian gerbil sensitive to a variety of stimuli. The only species, however, in which the reflex seizures and EEG findings are similar to those in humans is the baboon Papio papio extensively studied by Naquet and co-workers, although the light-induced epileptic discharges in baboons occur in the frontorolandic area rather than in the occipital lobe (reviewed by Menini and Silva-Barrat, 1998).

In humans, studies in subjects sensitive to flashing light and to striped patterns have yielded important information about reflex seizure triggering which also has direct implications for patient care and for prevention of visually-induced seizures in daily life. These findings (reviewed by Binnie and Wilkins, 1998; Zifkin and Kasteleijn-Nolst Trenité, 2000) also have implications for our understanding of what are now thought of as generalized epilepsies. They can also be applied to other reflex epilepsies and seizures and may represent a common mechanism of reflex seizure genesis. Recruitment of a “critical mass” of epileptogenic cortex in response to the reflex seizure stimulus can result in epileptiform EEG activity or a clinical seizure. This recruitment can be understood as relatively direct in some, but in other cases may involve the participation and interaction of several cortical areas or of cortex and subcortical structures activated by the external trigger. Other factors may have the opposite effect, reducing the amount of involved cortex and the likelihood that a seizure will occur.

The model of human pattern-sensitive epilepsy is of special interest because it shows that generalized clinical events and generalized or bilateral EEG abnormalities can be activated by a specific functional stimulation with a known localization. This electroclinical pattern is found in many subjects with several types of reflex seizure triggers and idiopathic generalized epilepsy (IGE), without neurologic deficit or evident lesions on imaging and who are thus presumed to have diffuse cortical hyperexcitability with a genetic component. Seizures induced by thinking, by “praxis”, and some cases of reading epilepsy appear to follow this model. Photosensitive occipital partial seizures also occur in patients with IGE (Guerrini et al., 1995; see chapter XXX), and motor activity can elicit seizures in nearly 50% of patients with JME (Matsuoka et al., 2000; see chapter YYY), which is now classified under “Idiopathic generalized epilepsies with variable phenotypes.” These and other observations in both reflex and spontaneous epileptogenesis suggest that the postulated diffuse cortical hyperexcitability in IGE is not necessarily uniform: specific activities can activate specific cortical systems or functional networks spread over several cortical regions in one or both hemispheres and produce focal or regional discharges, or partial seizures, which may generalize. This does not invalidate a diagnosis of underlying generalized epilepsy but shows that the biological substrate of generalized epilepsy can be complex. As predicted by Clementi’s model, focal or regional brain lesions can also be associated with reflex seizure triggering by appropriate stimuli. Such patients may also have spontaneous seizures, and many have neurologic deficit and abnormal imaging.

It may be clinically useful to think of precipitating stimuli for reflex seizures grouped according to their association with clinically generalized or bilateral EEG abnormalities, or with focal EEG abnormalities although this distinction does not constitute an element of the current proposed classification. This is summarized in Tables 1 and 2.

TABLE 1
REGIONAL OR FUNCTIONAL REFLEX TRIGGERS IN PATIENTS WITH GENERALIZED EPILEPTIFORM ACTIVITY (after Wolf, 1994)

TABLE 2: REGIONAL OR FUNCTIONAL REFLEX TRIGGERS IN PATIENTS WITH UNDERLYING FOCAL EPILEPSY

Seizures triggered by visual stimuli

Seizures triggered by visual stimuli are seen in several epilepsy syndromes. These include Idiopathic generalized epilepsies with variable phenotypes, most typically with JME, Idiopathic photosensitive occipital lobe epilepsy, “other” visual sensitive epilepsies, and the rarer progressive myoclonus epilepsies. Similar attacks may be triggered transiently in some metabolic encephalopathies such as alcohol withdrawal without requiring a diagnosis of epilepsy. Seizure types are discussed in Chapter X and the seizures of photosensitive occipital lobe epilepsy are discussed in Chapter Y. The seizures triggered by flicker and pattern are similar and can occur in some subjects with exposure to everyday visual stimuli. Patients may also induce seizures with manoeuvres which produce flicker, or with ocular movements. Self-induced visual-evoked seizures may be very difficult to treat. The attacks may be pleasurable. Some patients who note a refractory period after a reflex seizure will induce an attack to avoid a later one at a less convenient or safe time. Thus, noncompliance is common. There is clear secondary gain for some patients (Binnie 1988; Tassinari et al 1998). Some flashing colours, most commonly long wavelength red or red-cyan flicker, are more effective than white flashes in triggering EEG abnormalities (Shirakawa et al., 2001). This form of light sensitivity is not assessed in routine EEG evaluations but is of clinical significance because of the potency of these stimuli to trigger seizures in predisposed subjects who are exposed to them in everyday life. Regulations in some countries prohibit broadcasting certain types of patterned or flashing stimuli to prevent seizures (see Chapter X).

Seizures induced by thinking

Seizures induced by thinking (Wilkins et al 1982; Goossens et al 1990, Andermann et al., 1998) (“noögenic epilepsy”) occur in response to nonverbal higher cortical function and have been reported with a variety of stimuli, including arithmetic, drawing, playing cards or chess, decision-making, and solving Rubik's cube. These seizures do not typically appear to be activated by reading, writing, or by explicitly verbal tasks, but about 80% of patients are found to have more than one effective trigger. Seizures can be triggered in at least some of these patients without any real or contemplated movement of the hands, e.g., by a task requiring a spoken answer to an orally presented arithmetic or spatial problem. Unlike in primary reading epilepsy, most have spontaneous seizures. The reflex and spontaneous attacks include bilateral myoclonus, absences, and generalized tonic-clonic seizures and almost all reported patients have had generalized convulsions. Often these begin after a period of myoclonic jerks, but myoclonic jerks occurred without a following convulsion in 76% of patients reviewed by Andermann et al. (1998) and 60% of patients had absence seizures often associated with myoclonic jerks. Pure absence epilepsy with seizures triggered by thinking was not seen, but not all patients had myoclonus although some probably had JME. Myoclonic jerks and absence attacks may be ignored or unreported until a generalized seizure occurs and the patient then comes to medical attention. Seizures induced by thinking usually occur in the context of a generalized epilepsy. Partial seizures and clear focal EEG abnormalities have been reported but are the exception. The essential component in the seizure trigger appears to be nonverbal thought, the processing of numeric or spatial information, and possibly sequential decision making.

Seizures induced by thinking are typically associated with both spontaneous and evoked generalized or bilateral synchronous spike or multiple spike and wave complexes. They may only appear after reduction of medications in some patients. Although occasional patients have temporoparietal or frontal spontaneous EEG abnormalities, typically over the right side, these are at times mixed with generalized epileptiform activity. (Beaumanoir et al 1989; Goossens et al 1990).

Praxis Induction

This term was introduced by Japanese authors who described seizures triggered by thinking about “complicated spatial tasks in a sequential fashion, [making] decisions, and practically responding by using a part of [the] body” (Inoue, 2001). Writing is reported to be a major precipitating factor (Inoue et al., 1994) although reading is not. Hand or finger movements without “action-programming activity” (defined as “higher mental activity requiring hand movement” and apparently synonymous with praxis) are not effective triggers (Matsuoka et al., 2000). Reflex upper limb myoclonus occurs, and may spread. This pattern occurs almost exclusively in JME. It does not seem prominent in patients with thinking-induced seizures who do not also have prominent myoclonic reflex attacks. In its milder or most restricted forms, such as the morning myoclonic jerk of the arm manipulating a utensil (Seino M, personal communication, Bethel-Bielefeld 1999), this phenomenon resembles cortical reflex myoclonus as part of a “continuum of epileptic activity centered on the sensorimotor cortex” (Vignal et al., 1998). The motor component, either imagined or performed, is crucial in praxis-induction but other patients with seizures induced by thinking are activated by tasks such as purely mental calculation of orally-presented arithmetic tasks with no motor component in either the stimulus or the response. The pattern of praxis-induction fits well with JME, in which there is apparent regional hyperexcitability of sensorimotor cortex within an apparently generalized epileptic disorder, (discussed by Wolf, 1994) and possibly relevant morphologic abnormalities involving the motor system as well (Woermann et al., 1998).

Seizures triggered by reading

Seizures of primary reading epilepsy are described and possible mechanisms discussed in Chapter XX. Secondary reading epilepsy occurs in patients with spontaneous seizures. Activation by reading or other language tasks is found in both idiopathic and symptomatic epilepsies. Typically there is no jaw jerking, and the baseline EEG is often abnormal. Language-induced epilepsy involves seizure precipitation by speaking, reading, and writing (Geschwind and Sherwin 1967). The seizures may be similar to those of primary reading epilepsy, and some patients report only a single effective trigger (e. g., recitation alone) (Herskowitz et al 1984). Activation by reading and by other language tasks in the same patient can also occur in symptomatic epilepsies, as recently illustrated (with video documentation) by Canevini et al. (2001).

Language-induced epilepsy is not yet sufficiently well defined to warrant classification as a separate syndrome independent of reading epilepsy. Reported cases are more heterogeneous than those of primary reading epilepsy, whose definition should perhaps be expanded to include them. Alternatively, primary reading epilepsy could at some time be included as a variety of a more broadly defined language-induced epilepsy as suggested by Koutroumanidis and colleagues (Koutroumanidis et al 1998).

Seizures induced by somatosensory stimuli

Seizures induced by somatosensory stimulation are typically triggered by tapping, rubbing, or pricking part of the body. A localized or regional hypersensitive trigger zone can often be defined. The seizures begin with sensory symptoms; a sensory jacksonian seizure occurs often followed by tonic motor manifestations suggesting a supplementary motor area seizure. Subsequent generalization may occur. Consciousness is preserved at least at the onset. These typically occur in patients with postrolandic cortical lesions which may be subtle. Normal MR imaging has been reported in such patients with “rub” epilepsy but detailed imaging was not described (Kanemoto et al., 2001). The authors grouped these seizures, startle epilepsy, and seizures triggered by toothbrushing as “somatosensory evoked reflex epilepsies.” This does not reflect current classification but emphasizes the need to distinguish these patterns from each other. Drugs for partial seizures are needed, but seizures may be intractable and require evaluation for surgery.
Seizures induced by somatosensory stimuli must also be distinguished from nonepileptic events. Confusion with startle epilepsy (Chapter __) is unlikely if an adequate history is obtained.

Seizures induced by tapping, often by a single touch, also occur (“tap epilepsy”, reviewed by Deonna, 1998). These are typically manifestations of an idiopathic generalized epilepsy, rather than of the focal symptomatic or cryptogenic process usual in the seizures induced by somatosensory stimuli described above or of the severe static encephalopathy typical of startle epilepsy. They consist of brief reflex generalized myoclonic attacks associated with bilateral spike and wave EEG discharges and are not remarkably different from the “Benign early infantile reflex absence seizures” illustrated (with video recording) by Voskuil (2002). These occur typically in normal infants and toddlers, and can represent an idiopathic and relatively benign generalized myoclonic epilepsy syndrome rather than a progressive myoclonic encephalopathy. These seizures usually respond to valproate but may be self-limited. Prolonged treatment may thus not be needed.

Seizures induced by proprioceptive stimulation

Reflex attacks apparently induced by movement were reported over 100 years ago (Gowers 1901). Although early reports described attacks apparently induced by movement (Lishman et al., 1962), later work demonstrated the paramount role of proprioceptive afferents (Chauvel and Lamarche 1975). Thus, seizures originally described as movement-induced or gait-induced are usually more accurately described as “proprioceptive-induced.” These reflex seizures are rare, though well-described, and recently have been reviewed by Vignal and colleagues (Vignal et al 1998). Reflex drop attacks elicited by walking (Di Capua et al., 1989) are seen rarely in patients with reflex interictal spikes evoked by percussion of the foot (De Marco and Tassinari, 1981). We consider these to be a variety of seizures induced by proprioceptive stimulation, interesting because, unexpectedly, individuals with the interictal evoked spikes do not usually have such attacks. This disorder likely represents a form of idiopathic localization-related epilepsy of childhood, distinct because of the parietal lobe involvement. Participation of a more elaborate network involved in motor programming cannot be excluded in some cases especially if the effective stimulus seems restricted to activities such as walking although “gait epilepsy” (Iriarte et al., 2001) is not now a recognized seizure type or epilepsy syndrome.

Proprioceptive-induced seizures are evoked by passive or active movement without startle. The seizures are usually brief tonic seizures or simple partial attacks induced by active or passive movement of a limb and usually occur in subjects with fixed cerebral lesions and motor deficit. They may begin with a jacksonian pattern of sensory manifestations. They have been described as a transient phenomenon during nonketotic hyperglycemia, resolving with metabolic correction (Brick et al 1989) and as self-induced seizures with compulsive proprioceptive self-stimulation (Guerrini et al 1992). The epileptic nature of these attacks has been confirmed by ictal EEG recording (Arseni et al 1967).

Proprioceptive-induced seizures classically involve the rolandic sensorimotor area of the hemisphere contralateral to the clinical seizure onset. Maximum EEG electronegativity appears to be at the central vertex electrode in a published EEG record of seizures induced by walking (Iriarte et al 2001). The supplementary motor area may also be involved. This localization has been confirmed by imaging and intensive monitoring. Cerebral lesions are often evident and may have occurred well before the onset of attacks. In cases with nonketotic hyperglycemia, an associated neurologic deficit related to a remote lesion may be transiently unmasked during the period of seizures (Brick et al 1989). Acute cerebral lesions or diffuse encephalopathies may also be accompanied by self-limited proprioceptive-induced seizures.

Proprioceptive-induced seizures have been studied with a chronic alumina focus in one foot area of the monkey brain. Reflex seizures were elicited by stimuli that produced proprioceptive input to the hyperexcitable cortical area. Seizures could not be elicited after curarization (Chauvel and Lamarche 1975). Transcortical reflex loops appear to be involved in generating the proprioceptive-induced motor response in the cat with a penicillin focus (Giovanni et al 1983). Human proprioceptive-induced seizures are seen during nonketotic hyperglycemia, in which attacks are induced by active or passive limb movement and more rarely with conjugate gaze (Brick et al 1989; Duncan et al 1991). Many patients have fixed or transient neurologic deficits, suggesting a mechanism similar to that described for the monkey.

Proprioceptive-induced seizures should not be confused with startle epilepsy (Chapter _). In subjects with gross cerebral damage, the nature and localization of brain lesions are similar in the two syndromes, but the nature of the triggering stimulus is quite different. Proprioceptive-induced seizures begin less suddenly and may have initial jacksonian sensory manifestations. Proprioceptive-induced seizures can usually be distinguished from paroxysmal kinesigenic dystonia (choreoathetosis), characterized by dystonic and choreoathetoid movements, preserved consciousness, and a normal EEG during brief attacks which are rapidly induced by movement (Cler et al 1990). Paroxysmal kinesigenic dystonia is often familial, begins in neurologically normal children or young adults without evident lesions, and may be a channelopathy (Bhatia 1999). Spontaneous improvement often occurs.

Acutely ill patients with these seizures require urgent investigation for hyperglycemia and other encephalopathies. Seizures with nonketotic hyperglycemia resolve with successful treatment of the hyperglycemia. Recent or remote cerebral lesions often coexist with acute-onset proprioceptive-induced seizures. CT or MRI studies are urgently indicated in all such patients. Other patients with chronic proprioceptive-induced seizures require imaging studies to localize any treatable lesion that may be responsible for the attacks. Such lesions may be small, and detailed MRI may be needed. The history will allow tailoring of the EEG investigation. Seizures can be induced easily for study in the EEG laboratory, though reduction of medication may be needed. If proprioceptive activation is suspected in drop attacks, EEG monitoring of percussion of the sole of the foot with a reflex hammer (Tassinari et al 1988) may be helpful. This easy and brief test is worth performing in patients suspected of proprioceptive-induced seizures. Chronic proprioceptive-induced seizures in medically stable patients are usually manifestations of remote nonprogressive lesions as described above. As in other patients with seizures, a progressive lesion such as tumor must be excluded. Chronic (Rasmussen) encephalitis may also give rise to proprioceptive-induced seizures.

Proprioceptive-induced seizures without acute illness are rare and their prognosis unclear. There is no consensus as to their treatment. New onset proprioceptive-induced seizures with acute cerebral lesions may cease over days or weeks on their own and may require no specific treatment. Carbamazepine would be a rational first choice if medication is needed and clobazam (not available in the United States) may be added if necessary. Surgery has been reported as effective, but there has been no published series evaluating outcome in such patients (Falconer et al 1963).

Seizures induced by eating

Seizures induced by eating are characterized by seizures closely related to one or several parts of eating. The clinical triggers of a seizure are usually stereotyped for each patient, but patients may have some points in common. Rare patients have seizures at the very sight or smell of food; others may have them immediately after a heavy meal suggesting gastric distension as a trigger in such cases (Gastaut and Poirier, 1964). Seizures with eating are typically focal motor seizures, with or without auras or automatisms of temporolimbic type, almost always related to a symptomatic epilepsy. Seizures induced by eating are usually associated with localized or regional EEG epileptiform activity either from temporolimbic structures or from suprasylvian regions in association with larger lesions. EEG epileptiform activity that is generalized from the start is rare.

Rémillard and associates suggested that patients with temporolimbic seizures activated by eating have fewer spontaneous attacks and are more likely to have such attacks from the onset of their epilepsy than are patients with extralimbic, usually suprasylvian, seizure onset who have less constant activation by eating. Patients with suprasylvian seizure onset usually have more obvious extratemporal structural lesions and possible activation by specific thalamocortical afferents (Rémillard et al 1998). They may also have seizures with other forms of buccal stimulation such as tooth brushing or kissing. Koutroumanidis et al (2001) reported a case of adult-onset sensitivity to toohbrushing only, with normal imaging and interictal left frontal epileptiform activity and suggested that this was a cryptogenic reflex epilepsy.

Many patients with eating epilepsy have seizures that can be activated only by obvious combinations of stimuli (Fiol et al 1986), and alerting stimuli have been reported to abolish attacks (Ganga et al 1988), providing at least circumstantial evidence for involvement of an increasing cortical mass and of subcortical influences, which may promote or inhibit seizure occurrence in some cases of reflex epilepsy. It appears that localization of seizure onset and the nature of the seizure trigger are related in these attacks. Patients with suprasylvian lesions may be triggered by other oral activities and may represent a particularly noticeable type of seizure induced by proprioceptive or by somatosensory stimulation. They may be different from patients with temporolimbic-onset seizures, in whom taste and autonomic afferents may play a more important role, and in some of whom seizures may also be related to emotional or autonomic components of eating or to gastric distension, with possible participation of limbic and autonomic afferents.

A prevalence of approximately 1 per 1000 to 2000 epileptic patients has been reported (Vizioli 1962; Nagaraja and Chand 1984). The unusually high figures reported for Sri Lanka (Senanayake 1990) seem related to an idiosyncratic definition and to ascertainment methods.

It is our impression that patients with eating epilepsy and extralimbic seizure onset are more sensitive to either somatosensory or proprioceptive stimuli during eating and are more likely to report that seizure induction can be prevented by altering the sensory characteristics of their food. Some will drink through a straw rather than from a cup or avoid biting into a whole fruit by cutting it into small pieces. Stimulus alteration can reduce seizure frequency in what can otherwise be an intractable or socially disabling condition. Some patients take advantage of a refractory postictal period by inducing a seizure to avoid a later attack in an embarrassing setting. Drugs effective for partial seizures are necessary but medically intractable cases should be recognized early and assessed for surgical treatment.

Seizures triggered by music

Musicogenic epilepsy is characterized by seizures induced by hearing certain sounds, typically music (Critchley, 1977). Seizures have also been reported while the subject is exposed to the musical trigger during sleep or while merely thinking about it. The effective stimulus can be stereotyped for each patient and at times is exquisitely specific, but with no clear common pattern between patients. An affective component of the stimulus is evident in some patients, yet nonmusical sounds, such as whirring machinery, can be effective triggers in others. The seizures are of simple or complex partial type, with interictal and ictal epileptiform activity recorded from either temporal region (Scott, 1977), usually the right. Most patients also have spontaneous seizures and reflex seizures often begin over a year after the onset of spontaneous attacks (Wieser, 1997).

The pathophysiology of musicogenic epilepsy is frustratingly obscure. A conditioned response has been suggested to explain some cases of seizure induction by music (Shaw and Hill 1947), but this view is not now generally accepted (Forster 1972). Wieser and colleagues (1997) suggest a right temporal predominance and documented right anterior and mesial hyperperfusion during ictal SPECT as did Genc et al (2001). No depth electrode or electrocorticographic details have been published. Chronic temporal lobe depth electrode studies in epileptic subjects without musicogenic epilepsy suggest different lateralizations for different components of a musical stimulus (Wieser and Mazzola 1986). Creutzfeldt and Ojemann confirmed that musical stimuli may have widespread effects on neuronal activity in human temporal lobes extending well beyond the rather restricted primary auditory area (Creutzfeldt and Ojemann 1989; Liegeois-Chauvel et al 1991), that different components of music have different effects possibly with specialized lateralization and localization, and that the effects of music are different from those of speech. PET studies in patients and others (reviewed by Johnsrude et al., 2002) show predominant involvement of right hemisphere structures in networks involved in processing musical information, extending well beyond the classical auditory cortex of Heschl’s gyrus. Studies in subjects with musical hallucinations show that the primary auditory cortex is not “a sufficient substrate for higher-order pattern perception” (Griffiths, 2000). The primate auditory cortex is considered to consist of a central core of primary cortex which receives thalamic projections and which is linked to several “belt” areas. Primary cortex has multiple tonotopically organized sections and is especially sensitive to pure tones. Belt regions show more sensitivity to complex stimuli and are less tonotopically organized (reviewed by Johnsrude et al., 2002). Zifkin and Zatorre also note that more complex musical processing tasks activate more cortical and subcortical territory bilaterally but with right hemisphere predominance (Zifkin and Zatorre , 1998). Thus, hyperexcitable cortical areas could be stimulated to different degrees and extents by different musical stimuli in patients sensitive to musical triggers. Gloor (1990) suggested that responses to limbic stimulation in epileptic subjects depend on widespread neuronal matrices linked through connections which have become strengthened through repeated use, of interest in considering the delay from seizure onset to the development of sensitivity to music.

Seizures triggered by hot water

Seizures triggered by exposure to hot water are rare and until recently most cases were reported from India where attacks occurred during ritual bathing which involves pouring hot water over the head from a jug. Hot baths have also been implicated. Partial seizures occur, which may generalize. Differential diagnosis includes startle events, syncope, and febrile seizures. Many cases have been self-limited and appear to represent situation-related seizures akin to benign febrile seizures (Satishchandra et al., 1998) and while the outcome is often benign, some patients later develop more typical temporal lobe seizures. Some patients report pleasurable feelings with these events and self-induction has been reported. Initial treatment is by reducing the water temperature. More recent reports (Ioos et al., 2000; Bebek et al., 2001) report onset from infancy to adult life and spontaneous seizures in 62% of patients in whom onset was after infancy. Interictal EEG abnormalities have been recorded over temporal areas in half of patients. Imaging has reportedly been unremarkable.

Startle seizures
These are discussed in Chapter __.

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