Innervation of the sternocleidomastoid and trapezius muscles by the accessory nucleus

Active inference, stressors, and psychological trauma: A neuroethological model of (mal)adaptive explore-exploit dynamics in ecological context

This paper offers a formal account of emotional inference and stress-related behaviour, using the notion of active inference. We formulate responses to stressful scenarios in terms of Bayesian belief-updating and subsequent policy selection; namely, planning as (active) inference. Using a minimal model of how creatures or subjects account for their sensations (and subsequent action), we deconstruct the sequences of belief updating and behaviour that underwrite stress-related responses - and simulate the aberrant responses of the sort seen in post-traumatic stress disorder (PTSD). Crucially, the model used for belief-updating generates predictions in multiple (exteroceptive, proprioceptive and interoceptive) modalities, to provide an integrated account of evidence accumulation and multimodal integration that has consequences for both motor and autonomic responses. The ensuing phenomenology speaks to many constructs in the ecological and clinical literature on stress, which we unpack with reference to simulated inference processes and accompanying neuronal responses. A key insight afforded by this formal approach rests on the trade-off between the epistemic affordance of certain cues (that resolve uncertainty about states of affairs in the environment) and the consequences of epistemic foraging (that may be in conflict with the instrumental or pragmatic value of 'fleeing' or 'freezing'). Starting from first principles, we show how this trade-off is nuanced by prior (subpersonal) beliefs about the outcomes of behaviour - beliefs that, when held with unduly high precision, can lead to (Bayes optimal) responses that closely resemble PTSD.

Eye movements differ between ictal ipsilateral and contralateral head turning

PURPOSE

This study evaluated the relation of head and eye movements during ictal ipsilateral and contralateral head turning in patients with focal epilepsies with regard to lateralization of the epileptogenic zone.

METHODS

We reviewed our database and identified patients with ictal head turning ipsilateral and contralateral to the seizure onset as defined by ictal EEG. Twenty-seven seizures of 19 consecutive patients with ipsilateral and 40 seizures of 32 patients with contralateral head turning were investigated. Twenty-four patients had temporal lobe epilepsy (TLE), and 27 patients had extratemporal or multifocal epilepsy.

KEY FINDINGS

Eye movement in the same direction preceded contralateral head turning in 90% (36 of 40 seizures) of the seizures, but this was the case in only 33% (9 of 27 seizures) of the ipsilateral ictal head turning. In contrary, head turning preceded the eye movements in 67% (18 of 27 seizures) of the ipsilateral ictal head turning and in only 10% of the contralateral head turning (p < 0.001). The results were similar in TLE and FLE.

SIGNIFICANCE

The sequence of head and eye movements is different in ictal ipsilateral and contralateral head turning movements which likely reflects different spread patterns of epileptic activity associated with activation of different generators. The analysis of eye movements adds to the lateralization of ictal head movements.

Evolutionary and developmental understanding of the spinal accessory nerve

The vertebrate spinal accessory nerve (SAN) innervates the cucullaris muscle, the major muscle of the neck, and is recognized as a synapomorphy that defines living jawed vertebrates. Morphologically, the cucullaris muscle exists between the branchiomeric series of muscles innervated by special visceral efferent neurons and the rostral somitic muscles innervated by general somatic efferent neurons. The category to which the SAN belongs to both developmentally and evolutionarily has long been controversial. To clarify this, we assessed the innervation and cytoarchitecture of the spinal nerve plexus in the lamprey and reviewed studies of SAN in various species of vertebrates and their embryos. We then reconstructed an evolutionary sequence in which phylogenetic changes in developmental neuronal patterning led towards the gnathostome-specific SAN. We hypothesize that the SAN arose as part of a lamprey-like spinal nerve plexus that innervates the cyclostome-type infraoptic muscle, a candidate cucullaris precursor.

Intracisternal cranial root accessory nerve schwannoma associated with recurrent laryngeal neuropathy

Intracisternal accessory nerve schwannomas are very rare; only 18 cases have been reported in the literature. In the majority of cases, the tumor origin was the spinal root of the accessory nerve and the tumors usually presented with symptoms and signs of intracranial hypertension, cerebellar ataxia, and myelopathy. Here, we report a unique case of an intracisternal schwannoma arising from the cranial root of the accessory nerve in a 58-year-old woman. The patient presented with the atypical symptom of hoarseness associated with recurrent laryngeal neuropathy which is noted by needle electromyography, and mild hypesthesia on the left side of her body. The tumor was completely removed with sacrifice of the originating nerve rootlet, but no additional neurological deficits. In this report, we describe the anatomical basis for the patient's unusual clinical symptoms and discuss the feasibility and safety of sacrificing the cranial rootlet of the accessory nerve in an effort to achieve total tumor resection. To our knowledge, this is the first case of schwannoma originating from the cranial root of the accessory nerve that has been associated with the symptoms of recurrent laryngeal neuropathy.

Transitional Nerve: A New and Original Classification of a Peripheral Nerve Supported by the Nature of the Accessory Nerve (CN XI)

Classically, the accessory nerve is described as having a cranial and a spinal root. Textbooks are inconsistent with regard to the modality of the spinal root of the accessory nerve. Some authors report the spinal root as general somatic efferent (GSE), while others list a special visceral efferent (SVE) modality. We investigated the comparative, anatomical, embryological, and molecular literature to determine which modality of the accessory nerve was accurate and why a discrepancy exists. We traced the origin of the incongruity to the writings of early comparative anatomists who believed the accessory nerve was either branchial or somatic depending on the origin of its target musculature. Both theories were supported entirely by empirical observations of anatomical and embryological dissections. We find ample evidence including very recent molecular experiments to show the cranial and spinal root are separate entities. Furthermore, we determined the modality of the spinal root is neither GSE or SVE, but a unique peripheral nerve with a distinct modality. We propose a new classification of the accessory nerve as a transitional nerve, which demonstrates characteristics of both spinal and cranial nerves.

Does the motor cortex influence denervation in ALS? EMG studies of muscles with both contralateral and bilateral corticospinal innervation

OBJECTIVES

To evaluate the pattern of degeneration of lower motor neuron progression in ALS in relation to the contralateral and ipsilateral corticospinal innervation of the tested muscles.

METHODS

EMG evaluation of the sternomastoid and trapezius muscles on one or both sides, and transcranial magnetic stimulation to record motor evoked responses from these muscles after ipsilateral and contralateral cortical stimulation. The sternomastoid muscle receives corticospinal input from both hemispheres, but the trapezius only a contralateral corticospinal innervation; however the power motor innervation of both these muscles is derived from the same spinal nucleus, and the same motor nerve. Seventy-five patients with ALS were studied at the time of diagnosis, and 54 control subjects, consisting of normal subjects and disease control subjects. MUP analysis and spontaneous activity were assessed.

RESULTS

We confirmed that the sternomastoid receives both contralateral and ipsilateral corticospinal innervation, and the trapezius usually only contralateral innervation. The MUP analysis revealed symmetric changes in sternomastoid and trapezius muscles, and both muscles were equally affected.

CONCLUSIONS

Our findings are in accord with the concept that LMN degeneration in ALS is related to local factors in the spinal cord.

SIGNIFICANCE

Our findings suggest that local factors in the spinal grey matter are important in causing LMN degeneration in ALS, but they do not rule out a corticomotoneuronal contribution.

The effect of physical and psychosocial loads on the trapezius muscle activity during computer keying tasks and rest periods

The overall aim was to investigate the effect of psychosocial loads on trapezius muscle activity during computer keying work and during short and long breaks. In 12 female subjects, surface electromyography (EMG) was recorded bilaterally from the upper trapezius muscle during a standardized one hand keying task-interspaced with short (30 s) and long (4 min) breaks-in sessions with and without a combination of cognitive and emotional stressors. Adding psychosocial loads to the same physical work did not increase the activity of the trapezius muscle on either the keying or the control side, both of which remained at median and static EMG activity levels of around 5% and 2.5% of the maximal voluntary electrical activity (EMG(max)), respectively. The difference between the keying and the control side was significant; and further the control side activity was significantly increased above resting level. During both short and long breaks, exposure to psychosocial loads also did not increase the activity of the trapezius muscle either on the side of the keying or the control hand. Of note is that during long breaks the muscle activity of the keying side as well as that of the control side remained at the same level as during the short breaks, which was increased above resting level. This was to be seen from the static and the median EMG activity levels as well as gap times, the overall mean values being: 0.4%EMG(max), 1.1%EMG(max), and 50% in gap time, respectively.

IN CONCLUSION

psychosocial loads are not solely responsible for increased non-postural muscle activity; and increasing the duration of breaks does not per se cause muscle relaxation.