Noun imageability and the temporal lobes

We used positron emission tomography to investigate brain activity in respo nse to hearing or reading nouns of varying imageability. Three experiments were performed. Activity increased with noun imageability in the left mid-f usiform gyrus, the lateral parahippocampal area in humans, and in the rostr al medial temporal lobes close to or within perirhinal cortex. The left mid -fusiform activation has been observed in previous imaging studies of singl e word processing. Its functional significance was variously attributed to semantic processing, visual imagery, encoding episodic memories, or the int egration of lexical inputs from different sensory modalities. These hypothe ses are not mutually exclusive. The more rostral medial lobe response to no un imageability has not been observed previously. However, lesions in perir hinal cortex impair knowledge about objects in nonhuman primates, and bilat eral rostral ventromedial temporal lobe potentials in response to object no uns were observed with human intracranial recordings. Imageable (object) no uns are learnt with reference to sensory experiences of living and non-livi ng objects, whereas acquisition of the meaning of low imageable (abstract) nouns is more dependent on their context within sentences. Parahippocampal and perirhinal cortices are reciprocally connected with, respectively, seco nd and third order sensory association cortices. We conclude that access to the representations of word meaning is dependent on heteromodal temporal l obe cortex, and that during the acquisition of object nouns one route is es tablished through ventromedial temporal cortical regions that have reciproc al connections with all sensory association cortices. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.