Dr. Hurley's talk

      Dr. Hurley’s talk was about PPA which is a degeneration of language network that leads to anomia (inability to name objects) and comprehension problems. PPA has been subdivided into three main categories: agrammatic (non-fluent) PPA-G, semantic PPA-S, and logopenic PPA-L. The first form of PPA, the agrammatic form is associated with poor grammar, inability to form syntactic structures of sentences. Another form, the semantic aphasia is manifested in comprehension problems, and logopenic aphasia is the most controversial one that is widely studied recently. Logopenic aphasia patients have good grammar and good comprehension of words but they are unable to repeat words, much like in conduction aphasia. 

      One of the techniques used by Dr. Hurey measured neural activity in PPA patients and that was EEG with the N400 ERP. N400 is a negative going potential that peaks around 400 ms after the stimulus; it is sensitive to word retrieval. It was observed that the amplitude of the N400 was bigger when the expected word appeared. In the matching test paradigm, a picture or word cue was presented, and participants had to press a button when the word matched that particular picture and another button when it did not. In order to get to the semantic level of PPA, investigators asked subjects to identify whether the semantic mismatch was related to the same category. 

      There was one interesting patient who said that she knew the name of the object but she just could not say it. She proved herself right by correctly writing down the name of the object on the paper. It was concluded that this patient had problem with the speech production, and the EEG showed a big N400, suggesting that she connected to the word but she could not verbalize it (impairment in the lexical access). The brain areas that are associated with three forms of PPA were identified. PPA-S patients showed more atrophy in the anterior temporal lobe, PPA-L displayed atrophy in the posterior part of the language network. 

      When Dr. Hurley wanted to correlate temporal pole with the ability of naming objects an interesting thing happened. He found inactivation of the temporal pole in the fMRI study, even though there was activation in the PET scan. This made him think of options other than his CaLLs model to explore PPA. He proposed a possibility of the disconnection syndrome-inability to read, write, understand and copy words, where the white matter is damaged between the Broca’s area and temporal pole and between the temporal pole and Wernicke’s area. As a good researcher, he took into consideration different possibilities and he did not stop at this point; he plans to do more research on PPA.