Comprehension of concrete and abstract words in patients with selective anterior temporal lobe resection and in patients with selective amygdalo-hippocampectomy.

The role of the anterior temporal lobe (ATL) in semantic memory is now firmly established. There is still controversy, however, regarding the specific role of this region in processing various types of concepts. There have been reports of patients suffering from semantic dementia (SD), a neurodegenerative condition in which the ATL is damaged bilaterally, who present with greater semantic impairment for concrete concepts than for abstract concepts, an effect known as reversal of the concreteness effect.

Cognitive neuroscience studies of semantic memory in Alzheimer's disease.

Semantic memory is the component of long-term memory that stores our concepts about the world. The disruption of semantic memory as a result of brain damage may have profound negative consequences on an individual's ability to name objects and process concepts. This can be disrupted as a result of many forms of brain damage, particularly Alzheimer's disease (AD).

Increased neural efficiency in the temporal association cortex as the result of semantic task repetition.

We examined the effect of semantic task repetition and of alternating between tasks on cerebral blood flow in three H(2) (15)O positron emission tomography experiments. We found that repeatedly performing semantic tasks resulted in a reduction in cerebral blood flow to the left temporal association cortex similar to that found in priming experiments even though here there was no repetition of stimuli. Although the same effect was found in two different tasks (word meaning judgments and picture naming), it was only present when the same task was repeated on consecutive scans and not when the subjects alternated from scan to scan between tasks.

rCBF to the hippocampal complex covaries with superior semantic memory retrieval.

The study of medial-temporal amnesics has established that much of the brain's store of general knowledge can be retrieved without the hippocampus. Several brain imaging studies, however, have reported that the hippocampus is active during the performance of semantic memory tasks. Although this activity may reflect memory encoding, it is also possible that it is due to the process of retrieving the semantic representations of the stimuli.

Establishing visual category boundaries between objects: a PET study.

Individuals with Alzheimer's disease (AD) often have problems in recognizing common objects. This visual agnosia may stem from difficulties in establishing appropriate visual boundaries between visually similar objects. In support of this hypothesis, showed that AD subjects have difficulties in establishing visual category boundaries between continuously graded shapes.

Common and constrasting areas of activation for abstract and concrete concepts: an H2 15O PET study.

Lesion studies indicate that the lateral and inferior temporal cortex is a critical area of semantic memory storage, but little is known about the cortical organization of semantics within this area. One proposition has been that dominant physical characteristics of objects (structure, motility) are determining factors. A positron emission tomography experiment using the H2(15)O bolus method was performed to test this hypothesis by contrasting activation for concrete and abstract concepts.