Transcortical sensory aphasia as a result of left frontal cortical-subcortical infarction. A case report

Aphasia Induced by Infratentorial Ischemic Stroke: Two Case Reports

Aphasia induced by an infratentorial stroke has rarely been reported, and its mechanism has not been fully identified. We evaluated two individuals who had been admitted to Saiseikai Kumamoto Hospital in Kumamoto, Japan, due to acute ischemic stroke in order to determine whether their aphasia was induced by an infratentorial stroke. The first patient, a 59-year-old man with a history of left parietal embolic stroke with very mild sequelae of anomia, developed Wernicke's aphasia, nonfluent speech, and right limb ataxia as a result of the stroke. The second patient, a 76-year-old woman with a history of chronic renal failure, experienced transcortical sensory aphasia and right one-and-a-half syndrome as a result of the stroke. Both patients' recent ischemic lesions were limited to the right cerebellar hemisphere and the right medial portion of the midbrain. However, SPECT showed low-uptake lesions in both patients' left cerebral hemisphere that did not include the recent ischemic lesions but that had spread to an extent that was difficult to be explained by the old or recent ischemic lesions and that might be responsible for their recent aphasia. We believe that the aphasia experienced by these two patients may have been caused by crossed cerebello-cerebral diaschisis.

Newer Paradigms in Language Neurobiology

The field of language research has seen tremendous progress in the last two decades. Advances in neuro-imaging and stimulation mapping have changed the way we conceive the neural basis of speech and language processing. In the past, the Wernicke-Lichtheim model was the most influential model explaining the neuro-anatomical basis of language. More recently, the concept of dual stream language processing has emerged, wherein separate dorsal and ventral networks are synergistically involved in phonological (sound to articulation) and semantic (sound to meaning) processing respectively. In this review article, we highlight new insights and approaches to the neurobiology of language, across different aspects of language processing like perception, comprehension, production, hemisphere lateralization, role of subcortical structures and effect of damage to language networks.

Current Controversies on Wernicke's Area and its Role in Language

PURPOSE OF REVIEW

The aim of the study is to assess historical anatomical and functional definitions of Wernicke's area in light of modern lesion and neuroimaging data.

RECENT FINDINGS

"Wernicke's area" has become an anatomical label usually applied to the left posterior superior temporal gyrus and adjacent supramarginal gyrus. Recent evidence shows that this region is not critical for speech perception or for word comprehension. Rather, it supports retrieval of phonological forms (mental representations of phoneme sequences), which are used for speech output and short-term memory tasks. Focal damage to this region produces phonemic paraphasia without impairing word comprehension, i.e., conduction aphasia. Neuroimaging studies in recent decades provide evidence for a widely distributed temporal, parietal, and frontal network supporting language comprehension, which does not include the anatomically defined Wernicke area. The term Wernicke's area, if used at all, should not be used to refer to a zone critical for speech comprehension.

Where is the semantic system? A critical review and meta-analysis of 120 functional neuroimaging studies

Semantic memory refers to knowledge about people, objects, actions, relations, self, and culture acquired through experience. The neural systems that store and retrieve this information have been studied for many years, but a consensus regarding their identity has not been reached. Using strict inclusion criteria, we analyzed 120 functional neuroimaging studies focusing on semantic processing. Reliable areas of activation in these studies were identified using the activation likelihood estimate (ALE) technique. These activations formed a distinct, left-lateralized network comprised of 7 regions: posterior inferior parietal lobe, middle temporal gyrus, fusiform and parahippocampal gyri, dorsomedial prefrontal cortex, inferior frontal gyrus, ventromedial prefrontal cortex, and posterior cingulate gyrus. Secondary analyses showed specific subregions of this network associated with knowledge of actions, manipulable artifacts, abstract concepts, and concrete concepts. The cortical regions involved in semantic processing can be grouped into 3 broad categories: posterior multimodal and heteromodal association cortex, heteromodal prefrontal cortex, and medial limbic regions. The expansion of these regions in the human relative to the nonhuman primate brain may explain uniquely human capacities to use language productively, plan, solve problems, and create cultural and technological artifacts, all of which depend on the fluid and efficient retrieval and manipulation of semantic knowledge.