Missing links: the functional unification of language and memory (L∪M)

The field of neurocognition is currently undergoing a significant change of perspective. Traditional neurocognitive models evolved into an integrative and dynamic vision of cognitive functioning. Dynamic integration assumes an interaction between cognitive domains traditionally considered to be distinct. Language and declarative memory are regarded as separate functions supported by different neural systems. However, they also share anatomical structures (notably, the inferior frontal gyrus, the supplementary motor area, the superior and middle temporal gyrus, and the hippocampal complex) and cognitive processes (such as semantic and working memory) that merge to endorse our quintessential daily lives. We propose a new model, "L∪M" (i.e., Language/union/Memory), that considers these two functions interactively. We fractionated language and declarative memory into three cognitive dimensions, Embodiment-Formulation-Internalization, that communicate reciprocally. We formalized their interactions at the brain level with a connectivity-based approach. This new taxonomy overcomes the modular view of cognitive functioning and reconciles functional specialization with plasticity in neurological disorders.

The relationship of bioelectric activity and structural changes in the hippocampus at pharmacoresistant temporal lobe epilepsy

Background. Epilepsy is one of the most common neurological diseases globally. The unified concept about the role of hippocampus in the development of pharmacoresistant temporal lobe epilepsy is currently missing. Patients with pharmacoresistant temporal lobe epilepsy is often carried out by invasive electrocorticography to identify an epileptic focus. Registration of bioelectric activity of the hippocampus and comparison of data from the MRI pattern of the patient will determine the neurophysiological correlates of structural changes in hippocampus.Objective. The aim of the work was to determine the neurophysiological correlates of structural changes in the hippocampus in patients with focally caused temporal lobe epilepsy.Design and methods. The study was based on the analysis of the results of extraoperative invasive monitoring of the bioelectrical activity of the cortex and hippocampal complex, performed in 19 patients with focally caused drug-resistant epilepsy. The quantitative analysis included 34 tracks of hippocampal activity.Results. A distinctive feature of the bioelectrical activity of the hippocampal complex with its structural damage is the stable dominance of delta activity, which makes up 40–45 % of the total spectrum power. When the hippocampal complex is included in the epileptic system, high-index epileptiform activity is recorded. In the absence of structural damage to the hippocampal complex, the pattern is predominantly formed by the activity of theta and alpha frequency ranges. However, in the group of patients with the absence of a neuroimaging picture of sclerotic changes in the hippocampus, in 63 % of cases, a neurophysiological pattern of “prolapse” was recorded on the electrocorticogram. The spontaneous activity of the hippocampus had a low coherent relationship with the parameters of activity in the cortex of the ipsilateral and contralateral temporal lobes.Conclusions. The electrophysiological correlate of MR-positive structural changes in the hippocampal complex in drug-resistant epilepsy is the pattern of “loss of bioelectric activity”. Spontaneous hippocampal activity is generated independently of activity in the cortex of the ipsilateral and contralateral temporal lobes.

Multicentric tracking of multiple agents by anterior cingulate cortex during pursuit and evasion

Successful pursuit and evasion require rapid and precise coordination of navigation with adaptive motor control. We hypothesize that the dorsal anterior cingulate cortex (dACC), which communicates bidirectionally with both the hippocampal complex and premotor/motor areas, would serve a mapping role in this process. We recorded responses of dACC ensembles in two macaques performing a joystick-controlled continuous pursuit/evasion task. We find that dACC carries two sets of signals, (1) world-centric variables that together form a representation of the position and velocity of all relevant agents (self, prey, and predator) in the virtual world, and (2) avatar-centric variables, i.e. self-prey distance and angle. Both sets of variables are multiplexed within an overlapping set of neurons. Our results suggest that dACC may contribute to pursuit and evasion by computing and continuously updating a multicentric representation of the unfolding task state, and support the hypothesis that it plays a high-level abstract role in the control of behavior.

The human hippocampus and its subfield volume across age, sex and APOE e4 status

Female sex, age and carriage of the APOE e4 allele are the greatest risk factors for sporadic Alzheimer's disease (AD). The hippocampus has a selective vulnerability to atrophy in ageing that may be accelerated in AD, including in those with increased genetic risk of AD. Within the hippocampal complex, subfields represent cytoarchitectonic and connectivity based divisions. The change in global hippocampal and subfield volume associated with sex, age and APOE e4 status in healthy ageing have not yet been established despite their potential to provide a sensitive biomarker of future vulnerability to AD. Here, we examined non-linear age, sex and APOE effects, and their interactions, on hippocampal and subfield volumes across several decades spanning mid-life to old age in 36 653 healthy ageing individuals. Hippocampal volume showed a marked reduction in APOE e4/e4 female carriers after age 65. Volume was lower in homozygous e4 individuals in specific subfields including the presubiculum, subiculum head, CA1 body, CA3 head and CA4. The findings demonstrate that in healthy ageing, two factors - female sex and APOE e4 status - confer selective vulnerability of specific hippocampal subfields to volume loss.