John Hughlings-Jackson's Writings on the Auditory Aura and Localization of the Auditory Cortex

Localizing and lateralizing value of auditory phenomena in seizures

BACKGROUND

Auditory seizures (AS) are a rare type of focal seizures. AS are classically thought to involve a seizure onset zone (SOZ) in the temporal lobe, but there remain uncertainties about their localizing and lateralizing value. We conducted a narrative literature review with the aim of providing an up-to-date description of the lateralizing and localizing value of AS.

METHODS

The databases PubMed, Scopus, and Google Scholar were searched for literature on AS in December 2022. All cortical stimulation studies, case reports, and case series were analyzed to assess for auditory phenomena that were suggestive of AS and to evaluate if the lateralization and/or localization of the SOZ could be determined. We classified AS according to their semiology (e.g., simple hallucination versus complex hallucination) and the level of evidence with which the SOZ could be predicted.

RESULTS

A total of 174 cases comprising 200 AS were analyzed from 70 articles. Across all studies, the SOZ of AS were more often in the left (62%) than in the right (38%) hemisphere. AS heard bilaterally followed this trend. Unilaterally heard AS were more often due to a SOZ in the contralateral hemisphere (74%), although they could also be ipsilateral (26%). The SOZ for AS was not limited to the auditory cortex, nor to the temporal lobe. The areas more frequently involved in the temporal lobe were the superior temporal gyrus (STG) and mesiotemporal structures. Extratemporal locations included parietal, frontal, insular, and rarely occipital structures.

CONCLUSION

Our review highlighted the complexity of AS and their importance in the identification of the SOZ. Due to the limited data and heterogeneous presentation of AS in the literature, the patterns associated with different AS semiologies warrant further research.

A brief history of cortical functional localization and its relevance to neurosurgery

Modern cortical mapping is a cornerstone for safe supratentorial glioma resection in eloquent brain and allows maximal resection with improved functional outcomes. The unlocking of brain functionality through close observation and eventually via cortical stimulation has a fascinating history and was made possible by contributions from early physician-philosophers and neurosurgery’s founding fathers. Without an understanding of brain function and functional localization, none of today’s modern cortical mapping would be possible.

Emergence of semiology in epileptic seizures

Semiology, the manifestation of epilepsy, is dependent upon electrical activity produced by epileptic seizures that are organized within existing neural pathways. Clinical signs evolve as the epileptic discharge spreads in both time and space. Studying the relation between these, of which the temporal component is at least as important as the spatial one, is possible using anatomo-electro-clinical correlations of stereoelectroencephalography (SEEG) data. The period of semiology production occurs with variable time lag after seizure onset and signs then emerge more or less rapidly depending on seizure type (temporal seizures generally propagating more slowly and frontal seizures more quickly). The subset of structures involved in semiological production, the "early spread network", is tightly linked to those constituting the epileptogenic zone. The level of complexity of semiological features varies according to the degree of involvement of the primary or associative cortex, with the former having a direct relation to peripheral sensory and motor systems with production of hallucinations (visual and auditory) or elementary sensorimotor signs. Depending on propagation pattern, these signs can occur in a "march" fashion as described by Jackson. On the other hand, seizures involving the associative cortex, having a less direct relation with the peripheral nervous system, and necessarily involving more widely distributed networks manifest with altered cognitive and/or behavioral signs whose neural substrate involves a network of cortical structures, as has been observed for normal cognitive processes. Other than the anatomical localization of these structures, the frequency of the discharge is a crucial determinant of semiological effect since a fast (gamma) discharge will tend to deactivate normal function, whereas a slower theta discharge can mimic physiological function. In terms of interaction between structures, the degree of synchronization plays a key role in clinical expression, as evidenced, for example, by studies of ictal fear-related behavior (decorrelation of activity between structures inducing "release" phenomena) and of déjà vu (increased synchronization). Studies of functional coupling within networks underlying complex ictal behavior indicate that the clinical semiology of a given seizure depends upon neither the anatomical origin of ictal discharge nor the target areas of its propagation alone but on the dynamic interaction between these. Careful mapping of the ictal network in its full spread offers essential information as to the localization of seizure onset, by deducing that a given network configuration could only be generated by a given area or group of areas.

What makes a simple partial seizure complex?

The assessment of ictal consciousness has been the landmark criterion for the differentiation between simple and complex partial seizures over the last three decades. After review of the historical development of the concept of "complex partial seizure," the difficulties surrounding the simple versus complex dichotomy are addressed from theoretical, phenomenological, and neurophysiological standpoints. With respect to consciousness, careful analysis of ictal semiology shows that both the general level of vigilance and the specific contents of the conscious state can be selectively involved during partial seizures. Moreover, recent neuroimaging findings, coupled with classic electrophysiological studies, suggest that the neural substrate of ictal alterations of consciousness is twofold: focal hyperactivity in the limbic structures generates the complex psychic phenomena responsible for the altered contents of consciousness, and secondary disruption of the network involving the thalamus and the frontoparietal association cortices affects the level of awareness. These data, along with the localization information they provide, should be taken into account in the formulation of new criteria for the classification of seizures with focal onset.

An unusual presentation of epilepsy

Objective:

To report a case of fluctuating hearing due to auditory aura, as an unusual presentation of temporal lobe epilepsy.

Methods:

Case report and review of English language literature on temporal lobe epilepsy and auditory aura.

Results:

A 31-year-old man presented with intermittent symptoms of bilateral fullness in the ears associated with deafness. He was subsequently diagnosed with temporal lobe epilepsy. Further enquiry revealed a family history of epilepsy.

Conclusion:

Auditory aura as a presentation of temporal lobe epilepsy is rarely encountered in otolaryngological practice. This case highlights the importance of obtaining detailed information on epilepsy, including any family history of epilepsy, as a routine part of history-taking in patients presenting with fluctuating hearing loss.

An approach to nineteenth-century medical lexicon: the term "dreamy state"

Hughlings-Jackson coined the concept of dreamy state: According to him, one of the sensations of a "dreamy state" was an odd feeling of recognition and familiarity, often called "deja vu". A clear sense of strangeness could also be experienced in the "dreamy state" ("jamais vu"). Jackson himself did not use these French terms, but he was quite clear about the vivid feelings of strangeness and familiarity, which can occur in both normal and pathological conditions. In order to explore some of the exchanges between medical and nonmedical vocabularies, we examine the historical origins of this technical concept. By basing the study on European (medical and nonmedical) literature of the nineteenth century, we review the first descriptions of this state and compare them with the famous Hughlings-Jackson definitions. It appears that this medical concept was partly borrowed from a wide cultural background before being rationally developed and reworked in the fields of neurology and psychiatry.

A comparison of auditory evoked potentials to acoustic beats and to binaural beats

The purpose of this study was to compare cortical brain responses evoked by amplitude modulated acoustic beats of 3 and 6 Hz in tones of 250 and 1000 Hz with those evoked by their binaural beats counterparts in unmodulated tones to indicate whether the cortical processes involved differ. Event-related potentials (ERPs) were recorded to 3- and 6-Hz acoustic and binaural beats in 2000 ms duration 250 and 1000 Hz tones presented with approximately 1 s intervals. Latency, amplitude and source current density estimates of ERP components to beats-evoked oscillations were determined and compared across beat types, beat frequencies and base (carrier) frequencies. All stimuli evoked tone-onset components followed by oscillations corresponding to the beat frequency, and a subsequent tone-offset complex. Beats-evoked oscillations were higher in amplitude in response to acoustic than to binaural beats, to 250 than to 1000 Hz base frequency and to 3 Hz than to 6 Hz beat frequency. Sources of the beats-evoked oscillations across all stimulus conditions located mostly to left temporal lobe areas. Differences between estimated sources of potentials to acoustic and binaural beats were not significant. The perceptions of binaural beats involve cortical activity that is not different than acoustic beats in distribution and in the effects of beat- and base frequency, indicating similar cortical processing.