Semantic memory: Which side are you on?

Abstract

We present two patients in whom the combination of lesion site and cognitive performance was uniquely informative about the organisation and functional anatomy of semantic memory. One had had a single lobar stroke with an unusual distribution, largely destroying the whole of the left temporal lobe ventral to the superior temporal sulcus. The other patient had had herpes simplex encephalitis with destruction that was confined to the left cerebral hemisphere. The lesion again mainly encompassed the left temporal lobe, but also extended to the left inferior frontal gyrus. Cognitive outcomes in the two patients were compared with each other and with published results from patients with semantic dementia. This is because, whereas the majority of semantic dementia patients present with more prominent atrophy of the left rostroventral temporal lobe, they invariably have a degree of atrophy in the mirror region on the right that progresses. Semantic dementia therefore provides no clear evidence about the specific role of the left rostroventral temporal lobe. The two patients showed a highly consistent cognitive profile. Their deficits were also similar in many respects to that observed in patients with mild-moderate semantic dementia, including severe anomia that was not resolved by phonological cues and impairment on non-verbal as well as verbal semantic tasks. Certain key features of the semantic dementia profile, however-including sensitivity to the familiarity and typicality of the stimulus materials-appeared only in tasks requiring verbal output in these two patients with unilateral left temporal lesions. Results in these cases provide some of the first definitive evidence regarding the specific functions of the left anterior temporal lobe.

Laterality of anterior temporal lobe repetitive transcranial magnetic stimulation determines the degree of disruption in picture naming

“…It is well established that semantic dementia patients with left-dominant ATL atrophy are markedly more anomic than those with right-lateralised damage, even when equating for the severity of their receptive semantic deficits (Lambon Ralph et al 2001 ). Similar effects have been observed in patients with ATL damage arising from unilateral resection (Lambon Ralph et al 2012 ; Drane et al 2008 , 2013 ) and other aetiologies (Acres et al 2009 ; Lambon Ralph et al 2010 ; Damasio et al 2004 ; Patterson et al 2015 ). Functional neuroimaging studies of semantic tasks that involve speech production also produce more left-lateralised pattern of ATL activation more than those that use receptive tasks (Rice et al 2015b ).…”

Linguistic Aspects of Primary Progressive Aphasia

“…Some forms of stroke and closed-head trauma may resemble svPPA, but these are easily distinguished because of their sudden onset and nonprogressive nature. Other causes of a pattern of semantic memory difficulty resembling svPPA include herpes encephalitis (Lambon Ralph et al 2007, Noppeney et al 2007, Patterson et al 2015), but this is often subacute in progression and associated with the stigma of an infection.…”

“…Disease associated with svPPA may begin in the left hemisphere, often spreading to involve the contralateral temporal lobe. Whereas some investigators emphasize the role of the left anterior temporal lobe in the semantic memory deficit of patients with svPPA (Patterson et al 2015), some functional anatomy studies appear to implicate the atrophic anterior and ventral temporal regions of the right hemisphere in the semantic deficits of svPPA patients as well (Lambon Ralph et al 2010a, Pobric et al 2007). …”

Hemispheric lateralization of semantic feature distinctiveness

“…Thus, it is unclear whether their deficit in accessing distinctive features reflects a left-hemisphere or a bilateral impairment. Indeed, there is a more general debate in the literature on semantic processing as to whether the integration of semantic features is restricted to the left hemisphere [3, 25] or whether both hemispheres contribute to the integration of semantic features [20, 28]. …”