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Phantom Limbs and Brain Plasticity in Amputees  

Tamar Makin and London Plasticity Lab

Phantom sensations are experienced by almost every person who has lost their hand in adulthood. This mysterious phenomenon spans the full range of bodily sensations, including the sense of touch, temperature, movement, and even the sense of wetness. For a majority of upper-limb amputees, these sensations will also be at times unpleasant, painful, and for some even excruciating to the point of debilitating, causing a serious clinical problem, termed phantom limb pain (PLP). Considering the sensory organs (the receptors in the skin, muscle or tendon) are physically missing, in order to understand the origins of phantom sensations and pain the potential causes must be studied at the level of the nervous system, and the brain in particular. This raises the question of what happens to a fully developed part of the brain that becomes functionally redundant (e.g. the sensorimotor hand area after arm amputation). Relatedly, what happens to the brain representation of a body part that becomes overused (e.g. the intact hand, on which most amputees heavily rely for completing daily tasks)? Classical studies in animals show that the brain territory in primary somatosensory cortex (S1) that was “freed up” due to input loss (hereafter deprivation) becomes activated by other body part representations, those neighboring the deprived cortex. If neural resources in the deprived hand area get redistributed to facilitate the representation of other body parts following amputation, how does this process relate to persistent phantom sensation arising from the amputated hand? Subsequent work in humans, mostly with noninvasive neuroimaging and brain stimulation techniques, have expanded on the initial observations of cortical remapping in two important ways. First, research with humans allows us to study the perceptual consequence of remapping, particularly with regards to phantom sensations and pain. Second, by considering the various compensatory strategies amputees adopt in order to account for their disability, including overuse of their intact hand and learning to use an artificial limb, use-dependent plasticity can also be studied in amputees, as well as its relationship to deprivation-triggered plasticity. Both of these topics are of great clinical value, as these could inform clinicians how to treat PLP, and how to facilitate rehabilitation and prosthesis usage in particular. Moreover, research in humans provides new insight into the role of remapping and persistent representation in facilitating (or hindering) the realization of emerging technologies for artificial limb devices, with special emphasis on the role of embodiment. Together, this research affords a more comprehensive outlook at the functional consequences of cortical remapping in amputees’ primary sensorimotor cortex.


Diatheses in Germanic  

Simon Kasper

An alternation between clauses is treated as a diathetical alternation (a) if one or more semantic roles associated with the main verb exhibit differential grammatical (i.e., morphological or syntactic) encoding, (b) if the overt lexical expressions have same lexical roots, and (c) if the clauses approximately share at least the meaning and truth conditions of the semantically less specific clause alternant. This qualifies as diathesis what has come to be known as the canonical passive, impersonal passive, non-canonical passive, pseudo-passive, anticausative, the dative alternation, and the locative alternation, among others. The focus of this article is on the semantic restrictions governing a clause’s participation in various diathetical alternations across the modern Germanic (standard) languages. Semantic differences between alternating clauses are captured using a sophisticated semantic role account. Grammatical encoding of diathesis is described in a theory-neutral manner using the four-case system of the old Germanic languages as a tertium comparationis and syntactic function notions from descriptive typology. Diatheses are differentiated by the semantic roles that are fore- and backgrounded by means of the syntactic functions they bear. The roles that alternate in grammatical coding are foregrounded in the clause in which they have the higher syntactic function in a syntactic function hierarchy, and they are backgrounded in the clause in which they have the lower syntactic function. In a first set of diatheses, alternations are described in which the proto-agent role is backgrounded and a proto-patient is foregrounded. This set includes a “patient passive” and the “anticausative domain.” In a second set of diatheses, the proto-agent is again backgrounded, but now the proto-recipient is foregrounded. This is illustrated using the “eventive recipient passive.” Completing this pattern, the “locational passive” represents a diathetical pattern in which the proto-agent role is backgrounded once more and the proto-locational role is foregrounded. Other types of diatheses in which the proto-locational is foregrounded and the proto-patient is backgrounded are exemplified by means of the location/possession alternation (dative alternation) and the location/affection alternation (e.g., locative and applicative alternations).