Abstract
Cortically projecting basal forebrain neurons play a critical role in learning and attention, and their degeneration accompanies age-related impairments in cognition. Despite the impressive anatomical and cell-type complexity of this system, currently available data suggest that basal forebrain neurons lack complexity in their response fields, with activity primarily reflecting only macro-level brain states such as sleep and wake, onset of relevant stimuli and/or reward obtainment. The current study examined the spiking activity of basal forebrain neuron populations across multiple phases of a selective attention task, addressing, in particular, the issue of complexity in ensemble firing patterns across time. Clustering techniques applied to the full population revealed a large number of distinct categories of task-phase-specific activity patterns. Unique population firing-rate vectors defined each task phase and most categories of task-phase-specific firing had counterparts with opposing firing patterns. An analogous set of task-phase-specific firing patterns was also observed in a population of posterior parietal cortex neurons. Thus, consistent with the known anatomical complexity, basal forebrain population dynamics are capable of differentially modulating their cortical targets according to the unique sets of environmental stimuli, motor requirements, and cognitive processes associated with different task phases.
Highlights
ENSEMBLE FIRING PATTERNS OF BASAL FOREBRAIN NEURONS DISTINGUISH ALL TASK PHASES One goal of the present work was to examine basal forebrain (BF) neuron activity patterns in relation to multiple phases of a selective attention task (Figure 1). The merit of this approach lies in the ability to better identify potential complexities in the response fields of BF neurons that cannot be achieved through examination of peri-event histograms
As a brain structure for which normal functioning is of critical importance to diverse cognitive processes, it is remarkable how few studies have examined the dynamics of BF neurons during behavioral task performance
Large ensemble recordings of BF neurons were obtained during performance of a selective attention task with the goal of filling, to some extent, this gap in knowledge
Summary
The basal forebrain (BF) of the mammalian brain is composed of several subcortical nuclei, bearing efferents which modulate responsiveness of their neocortical targets to their cortical and/or thalamic inputs (Bigl et al, 1982; Mesulam et al, 1983; Saper, 1984; Hasselmo and Barkai, 1995; Zaborszky et al, 1997, 1999; Disney et al, 2007; Goard and Dan, 2009; Bhattacharyya et al, 2013) The complexity of this projection system is relatively high in at least two ways. Anatomical specificity has been observed in the activation of prefrontal cortex-projecting vs. motor cortex-projecting BF acetylcholine (ACh) neurons during task performance (Parikh et al, 2007)
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