The cognitive neuroscience of aging is a large and diverse field seeking to understand cross-sectional differences and longitudinal changes in brain structure and function. Research in this field also investigates how brain differences or changes influence behavior in later life. There is consistent evidence indicating that cross-sectionally the brain is smaller in older adults (OA) relative to younger adults (YA), and this is due to longitudinal change over time. Furthermore, there are differences in functional activation patterns and the functional network architecture in the aging brain, both of which may contribute to the behavioral differences experienced by OA. Most notably, the differences in functional activation patterns suggest that perhaps the aging brain may compensate for the impacts of aging in an attempt to preserve performance. As such, several frameworks for understanding the processes of aging have taken hold resulting in testable hypotheses that link brain function and structure to behavior. Finally, in Alzheimer’s Disease, cognitive neuroscience methodologies have provided additional insights into the impacts of the disease on brain structure, function, and behavior.
Jessica A. Bernard and Tracey H. Hicks
Evangelia G. Chrysikou, Elizabeth Espinal, and Alexandra E. Kelly
Memory refers to the set of cognitive systems and the neural structures that support them that allow humans to learn from experience, leverage this knowledge to understand and guide behavior in the present, and use past memories to think about and plan for the future. Neuroscience research on learning and memory has leveraged advances in behavioral methods, structural and functional brain imaging, noninvasive brain stimulation, and lesion studies to evaluate synergies and dissociations among small- and large-scale neural networks in support of memory performance. Overall, this work has converged to a conceptualization of new memories as representations of distributed patterns of neural activity across cortical and subcortical brain systems that provide neural grounding of sensorimotor and perceptual experiences, actions, thoughts, and emotions, and which can be reinstated as a result of internal or external cues. Most of this literature has supported dissociations among working and long-term memory, as well as between procedural, episodic, and semantic memories. On the other hand, progress in human neuroscience methodologies has revealed the interdependence of these memory systems in the context of complex cognitive tasks and suggests a dynamic and highly interactive neural architecture underlying human learning and memory. Future neuroscience research is anticipated to focus on understanding the neural mechanisms supporting this interactivity at the cellular and systems levels, as well as investigating the time course of their engagement.
Wayfinding, like other related spatial cognitive abilities, is a core function of all mobile animals. The past 50 years have a seen a plethora of research devoted to elucidating the neural basis of this function. This research has led to the identification of neuronal cell types—many of which can be found within the hippocampal area and afferent brain regions—that encode different spatial variables and together are thought to provide animals with a so-called “cognitive map.” Moreover, seminal research carried out over the past decade has identified a neural activity event—known as “replay”—that is thought to consolidate newly formed cognitive maps, so to commit them to long-term storage and support planning of goal-directed navigational trajectories in familiar, and perhaps novel, environments. Finally, this hippocampal spatial coding scheme has in recent years been postulated to extend to nonspatial domains, including episodic memory, suggesting it may play a general role in knowledge creation.
Katherine E. Conen and Theresa M. Desrochers
Sequences of actions and experiences are a central part of daily life in many species. Sequences consist of a set of ordered steps with a distinct beginning and end. They are defined by the serial order and relationships between items, though not necessarily by precise timing intervals. Sequences can be composed from a wide range of elements, including motor actions, perceptual experiences, memories, complex behaviors, or abstract goals. However, despite this variation, different types of sequences may share common features in neural coding. Examining the neural responses that support sequences is important not only for understanding the sequential behavior in daily life but also for investigating the array of diseases and disorders that impact sequential processes and the impact of therapeutics used to treat them. Research into the neural coding of sequences can be organized into the following broad categories: responses to ordinal position, coding of adjacency and inter-item relationships, boundary responses, and gestalt coding (representation of the sequence as a whole). These features of sequence coding have been linked to changes in firing rate patterns and neuronal oscillations across a range of cortical and subcortical brain areas and may be integrated in the lateral prefrontal cortex. Identification of these coding schemes has laid out an outline for understanding how sequences are represented at a neural level. Expanding from this work, future research faces fundamental questions about how these coding schemes are linked together to generate the complex range of sequential processes that influence cognition and behavior across animal species.
Paul Cisek and David Thura
Making a good decision often takes time, and in general, taking more time improves the chances of making the right choice. During the past several decades, the process of making decisions in time has been described through a class of models in which sensory evidence about choices is accumulated until the total evidence for one of the choices reaches some threshold, at which point commitment is made and movement initiated. Thus, if sensory evidence is weak (and noise in the signal increases the probability of an error), then it takes longer to reach that threshold than if sensory evidence is strong (thus helping filter out the noise). Crucially, the setting of the threshold can be increased to emphasize accuracy or lowered to emphasize speed. Such accumulation-to-bound models have been highly successful in explaining behavior in a very wide range of tasks, from perceptual discrimination to deliberative thinking, and in providing a mechanistic explanation for the observation that neural activity during decision-making tends to build up over time. However, like any model, they have limitations, and recent studies have motivated several important modifications to their basic assumptions. In particular, recent theoretical and experimental work suggests that the process of accumulation favors novel evidence, that the threshold decrease over time, and that the result yields improved decision-making in real, natural situations.
Megan A.K. Peters
The human brain processes noisy information to help make adaptive choices under uncertainty. Accompanying these decisions about incoming evidence is a sense of confidence: a feeling about whether a decision is correct. Confidence typically covaries with the accuracy of decisions, in that higher confidence is associated with higher decisional accuracy. In the laboratory, decision confidence is typically measured by asking participants to make judgments about stimuli or information (type 1 judgments) and then to rate their confidence on a rating scale or by engaging in wagering (type 2 judgments). The correspondence between confidence and accuracy can be quantified in a number of ways, some based on probability theory and signal detection theory. But decision confidence does not always reflect only the probability that a decision is correct; confidence can also reflect many other factors, including other estimates of noise, evidence magnitude, nearby decisions, decision time, and motor movements. Confidence is thought to be computed by a number of brain regions, most notably areas in the prefrontal cortex. And, once computed, confidence can be used to drive other behaviors, such as learning rates or social interaction.
Corentin Gaillard and Suliann Ben Hamed
The brain has limited processing capacities. Attention selection processes are continuously shaping humans’ world perception. Understanding the mechanisms underlying such covert cognitive processes requires the combination of psychophysical and electrophysiological investigation methods. This combination allows researchers to describe how individual neurons and neuronal populations encode attentional function. Direct access to neuronal information through innovative electrophysiological approaches, additionally, allows the tracking of covert attention in real time. These converging approaches capture a comprehensive view of attentional function.
Tamar Makin and London Plasticity Lab
Phantom sensations are experienced by almost every person who has lost their hand in adulthood. This mysterious phenomenon spans the full range of bodily sensations, including the sense of touch, temperature, movement, and even the sense of wetness. For a majority of upper-limb amputees, these sensations will also be at times unpleasant, painful, and for some even excruciating to the point of debilitating, causing a serious clinical problem, termed phantom limb pain (PLP). Considering the sensory organs (the receptors in the skin, muscle or tendon) are physically missing, in order to understand the origins of phantom sensations and pain the potential causes must be studied at the level of the nervous system, and the brain in particular. This raises the question of what happens to a fully developed part of the brain that becomes functionally redundant (e.g. the sensorimotor hand area after arm amputation). Relatedly, what happens to the brain representation of a body part that becomes overused (e.g. the intact hand, on which most amputees heavily rely for completing daily tasks)? Classical studies in animals show that the brain territory in primary somatosensory cortex (S1) that was “freed up” due to input loss (hereafter deprivation) becomes activated by other body part representations, those neighboring the deprived cortex. If neural resources in the deprived hand area get redistributed to facilitate the representation of other body parts following amputation, how does this process relate to persistent phantom sensation arising from the amputated hand? Subsequent work in humans, mostly with noninvasive neuroimaging and brain stimulation techniques, have expanded on the initial observations of cortical remapping in two important ways. First, research with humans allows us to study the perceptual consequence of remapping, particularly with regards to phantom sensations and pain. Second, by considering the various compensatory strategies amputees adopt in order to account for their disability, including overuse of their intact hand and learning to use an artificial limb, use-dependent plasticity can also be studied in amputees, as well as its relationship to deprivation-triggered plasticity. Both of these topics are of great clinical value, as these could inform clinicians how to treat PLP, and how to facilitate rehabilitation and prosthesis usage in particular. Moreover, research in humans provides new insight into the role of remapping and persistent representation in facilitating (or hindering) the realization of emerging technologies for artificial limb devices, with special emphasis on the role of embodiment. Together, this research affords a more comprehensive outlook at the functional consequences of cortical remapping in amputees’ primary sensorimotor cortex.
Richard L. Doty
Decreased ability to smell is common in older persons. Some demonstrable smell loss is present in more than 50% of those 65 to 80 years of age, with up to 10% having no smell at all (anosmia). Over the age of 80, 75% exhibit some loss with up to 20% being totally anosmic. The causes of these decrements appear multifactorial and likely include altered intranasal airflow patterns, cumulative damage to the olfactory receptor cells from viruses and other environmental insults, decrements in mucosal metabolizing enzymes, closure of the cribriform plate foramina through which olfactory receptor cells axons project to the brain, loss of selectivity of receptor cells to odorants, and altered neurotransmission, including that exacerbated in some age-related neurodegenerative diseases.
Eliot A. Brenowitz
Animals produce communication signals to attract mates and deter rivals during their breeding season. The coincidence in timing results from the modulation of signaling behavior and neural activity by sex steroid hormones associated with reproduction. Adrenal steroids can influence signaling for aggressive interactions outside the breeding season. Androgenic and estrogenic hormones act on brain circuits that regulate the motivation to produce and respond to signals, the motor production of signals, and the sensory perception of signals. Signal perception, in turn, can stimulate gonadal development.