This article provides a classification of primary progressive aphasia (PPA) and its 3 main variants to improve the uniformity of case reporting and the reliability of research results. Criteria for the 3 variants of PPA-nonfluent/agrammatic, semantic, and logopenic-were developed by an international group of PPA investigators who convened on 3 occasions to operationalize earlier published clinical descriptions for PPA subtypes. Patients are first diagnosed with PPA and are then divided into clinical variants based on specific speech and language features characteristic of each subtype. Classification can then be further specified as "imaging-supported" if the expected pattern of atrophy is found and "with definite pathology" if pathologic or genetic data are available. The working recommendations are presented in lists of features, and suggested assessment tasks are also provided. These recommendations have been widely agreed upon by a large group of experts and should be used to ensure consistency of PPA classification in future studies. Future collaborations will collect prospective data to identify relationships between each of these syndromes and specific biomarkers for a more detailed understanding of clinicopathologic correlations. Neurology

Based on the recent literature and collective experience, an international consortium developed revised guidelines for the diagnosis of behavioural variant frontotemporal dementia. The validation process retrospectively reviewed clinical records and compared the sensitivity of proposed and earlier criteria in a multi-site sample of patients with pathologically verified frontotemporal lobar degeneration. According to the revised criteria, 'possible' behavioural variant frontotemporal dementia requires three of six clinically discriminating features (disinhibition, apathy/inertia, loss of sympathy/empathy, perseverative/compulsive behaviours, hyperorality and dysexecutive neuropsychological profile). 'Probable' behavioural variant frontotemporal dementia adds functional disability and characteristic neuroimaging, while behavioural variant frontotemporal dementia 'with definite frontotemporal lobar degeneration' requires histopathological confirmation or a pathogenic mutation. Sixteen brain banks contributed cases meeting histopathological criteria for frontotemporal lobar degeneration and a clinical diagnosis of behavioural variant frontotemporal dementia, Alzheimer's disease, dementia with Lewy bodies or vascular dementia at presentation. Cases with predominant primary progressive aphasia or extra-pyramidal syndromes were excluded. In these autopsy-confirmed cases, an experienced neurologist or psychiatrist ascertained clinical features necessary for making a diagnosis according to previous and proposed criteria at presentation. Of 137 cases where features were available for both proposed and previously established criteria, 118 (86%) met 'possible' criteria, and 104 (76%) met criteria for 'probable' behavioural variant frontotemporal dementia. In contrast, 72 cases (53%) met previously established criteria for the syndrome (P < 0.001 for comparison with 'possible' and 'probable' criteria). Patients who failed to meet revised criteria were significantly older and most had atypical presentations with marked memory impairment. In conclusion, the revised criteria for behavioural variant frontotemporal dementia improve diagnostic accuracy compared with previously established criteria in a sample with known frontotemporal lobar degeneration. Greater sensitivity of the proposed criteria may reflect the optimized diagnostic features, less restrictive exclusion features and a flexible structure that accommodates different initial clinical presentations. Future studies will be needed to establish the reliability and specificity of these revised diagnostic guidelines.

Sensory information undergoes extensive associative elaboration and attentional modulation as it becomes incorporated into the texture of cognition. This process occurs along a core synaptic hierarchy which includes the primary sensory, upstream unimodal, downstream unimodal, heteromodal, paralimbic and limbic zones of the cerebral cortex. Connections from one zone to another are reciprocal and allow higher synaptic levels to exert a feedback (top-down) influence upon earlier levels of processing. Each cortical area provides a nexus for the convergence of afferents and divergence of efferents. The resultant synaptic organization supports parallel as well as serial processing, and allows each sensory event to initiate multiple cognitive and behavioural outcomes. Upstream sectors of unimodal association areas encode basic features of sensation such as colour, motion, form and pitch. More complex contents of sensory experience such as objects, faces, word-forms, spatial locations and sound sequences become encoded within downstream sectors of unimodal areas by groups of coarsely tuned neurons. The highest synaptic levels of sensory-fugal processing are occupied by heteromodal, paralimbic and limbic cortices, collectively known as transmodal areas. The unique role of these areas is to bind multiple unimodal and other transmodal areas into distributed but integrated multimodal representations. Transmodal areas in the midtemporal cortex, Wernicke's area, the hippocampal-entorhinal complex and the posterior parietal cortex provide critical gateways for transforming perception into recognition, word-forms into meaning, scenes and events into experiences, and spatial locations into targets for exploration. All cognitive processes arise from analogous associative transformations of similar sets of sensory inputs. The differences in the resultant cognitive operation are determined by the anatomical and physiological properties of the transmodal node that acts as the critical gateway for the dominant transformation. Interconnected sets of transmodal nodes provide anatomical and computational epicentres for large-scale neurocognitive networks. In keeping with the principles of selectively distributed processing, each epicentre of a large-scale network displays a relative specialization for a specific behavioural component of its principal neurospychological domain. The destruction of transmodal epicentres causes global impairments such as multimodal anomia, neglect and amnesia, whereas their selective disconnection from relevant unimodal areas elicits modality-specific impairments such as prosopagnosia, pure word blindness and category-specific anomias. The human brain contains at least five anatomically distinct networks. The network for spatial awareness is based on transmodal epicentres in the posterior parietal cortex and the frontal eye fields; the language network on epicentres in Wernicke's and Broca's areas; the explicit memory/emotion network on epicentres in the hippocampal-entorhinal complex and the amygdala; the f...

The organization of projections from the cholinergic neurons of the basal forebrain to neocortex and associated structures was investigated in the rhesus monkey with the help of horseradish peroxidase transport, acetylcholinesterase histochemistry, and choline acetyltransferase immunohistochemistry. Four groups of neurons contained cholinergic perikarya and were designated as Chl-Ch4. The C h l group corresponds to the medial septa1 nucleus; about 105% of its neurons are cholinergic, and it provides a substantial projection to the hippocampus. The Ch2 group corresponds to the vertical nucleus of the diagonal band; a t least 70%' of its neurons are cholinergic, and it is the major source of innervation that the hippocampus and hypothalamus receive from the Chl-Ch4 complex. The Ch3 group most closely corresponds to the horizontal nucleus of the diagonal band; only 1 % of its neurons can definitely be shown to be cholinergic, and it is the major source of Chl-Ch4 projections to the olfactory bulb. The Ch4 group most closely corresponds to the nucleus basalis of Meynert; a t least 90% of its neurons are cholinergic, and it has projections to widespread areas of cortex and to the amygdala. In fact, the Ch4 group provides the single major source of cholinergic innervation for the entire cortical surface. In this respect, it is analogous to the raphe nuclei and to the nucleus locus coeruleus, which constitute the major sources of widespread cortical serotonergic and noradrenergic innervation, respectively.The extensive Ch4 group can be divided into several subdivisions. Each subdivision has a preferential set of targets for its projections even though the connection patterns contain considerable overlap. The anteromedial subdivision of Ch4 is the major source of cholinergic projections to areas on the medial aspect of the cerebral hemispheres: the anterolateral Ch4 subdivision is the major source of cholinergic projections to frontoparietal opercular areas and to the amygdala; the intermediate Ch4 subdivision provides the major cholinergic input for a variety of dorsal prefrontal, insular, posterior parietal, inferotemporal, and peristriate areas; and the posterior subdivision of Ch4 provides the major cholinergic innervation of superior temporal and immediately adjacent areas.

Stimulus-evoked neural activity is attenuated upon stimulus repetition ('repetition suppression'), a phenomenon attributed to largely automatic processes in sensory neurons. By manipulating the likelihood of stimulus repetition, we show that repetition suppression in the human brain is reduced when stimulus repetitions are improbable (and thus, unexpected). These data suggest that repetition suppression reflects a relative reduction in top-down perceptual 'prediction error' when processing an expected compared to an unexpected stimulus.Stimulus-specific repetition suppression (RS) -the relative attenuation in neural signal evoked by the repeated occurrence of a stimulus -is among the best-known neural phenomena [1][2][3][4] , and has been widely employed in functional magnetic resonance imaging (fMRI) studies to define functional properties of brain regions 5,6 and explore neural substrates of behavioral priming effects 2,4 . However, the neurocomputational basis for RS remains controversial 1 . Two influential theories view RS as a relatively automatic consequence of the bottom-up flow of perceptual information through sensory cortex: either neurons tuned to the repeated stimulus fatigue 1 , or subsequent presentations of a stimulus are encoded more sparsely (and efficiently), leading to a sharpening in the population of neurons recruited 4,7 . By contrast, a recent model of perceptual inference casts RS as a consequence of top-down perceptual expectations 2,8 : here, RS reflects a reduction in perceptual 'prediction error' (the neural signal evoked by a mismatch between expected and observed percepts) that occurs when sensory evidence conforms to a more probable (previously seen) compared to a less probable (novel) percept. Unlike other theories, the prediction error model holds that RS will vary with contextual factors that affect subjects' perceptual expectations, and suggests that RS will be reduced under conditions where stimulus repetitions are unexpected.We created such a situation by presenting subjects (n = 16), who had provided informed written consent, on each trial with either the same face twice, or two different faces, in two experimental contexts -one where repetitions occurred more frequently than alternations, and one where the reverse was the case. Importantly, all face exemplars were trial-unique, such that the NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript probability of a repetition per se, and not the frequency of repetition of a specific face, varied between blocks ( Fig. 1a and Supplementary Methods online). Incidental to this manipulation, subjects were required to make a speeded response to occasional inverted faces ('targets') 9 . Limiting our analysis to non-target trials, we measured how face-sensitive visual cortex responded to face repetitions ('rep trials') and face alternations ('alt trials') that were either expected (in 'REP BLOCKS') or unexpected (in 'ALT BLOCKS'), comparing these estimates in 2 × 2 factorial mixed block/event-related desi...