Project Summary Abstract. Conceptual or semantic knowledge refers to information about objects, actions, relations, self, culture, and includes meanings of words and phrases. The use of this knowledge is pervasive and automatic in daily life. Everyday activities such as communication, recognition and use of objects, social interactions, and decision making are crucially reliant on conceptual knowledge. Impairment of this complex and widely distributed system has serious consequences for quality of life. Several neurological and psychiatric disorders are associated with the impairment of this system, including stroke with aphasia, dementias, temporal lobe epilepsy, schizophrenia, and autism. Understanding the structure and organization of this system, and the specific ways it is disrupted in these individuals, is critical for developing better treatments and rehabilitation strategies. The goal of this research is to understand the structure and use of this information, its neural basis, and the ways in which it can be impaired by neuropathology. Here, we focus on a brain region that has emerged as a core component of the conceptual system: anterior temporal lobe. This brain region has been the subject of intense research for over two decades not just in semantics, but in a number of other domains such as social cognition, sentence processing, and naming of familiar people and places. This has generated a rich and complex set of findings, some of which are often difficult to reconcile with each other. Insights into the function of this region that can shed light on its role in myriad functions would clearly be very valuable. Using neuroimaging, transcranial magnetic stimulation, and studies of patients with stroke, we examine predictions of a novel theory that can account for many findings relating to the anterior temporal lobe. The proposed experiments will shed new light on the organization and function of this core semantic region in the healthy and impaired brain.