Are Bigger Brains Better?

Abstract

Attempts to relate brain size to behaviour and cognition have rarely integrated information from insects with that from vertebrates. Many insects, however, demonstrate that highly differentiated motor repertoires, extensive social structures and cognition are possible with very small brains, emphasising that we need to understand the neural circuits, not just the size of brain regions, which underlie these feats. Neural network analyses show that cognitive features found in insects, such as numerosity, attention and categorisation-like processes, may require only very limited neuron numbers. Thus, brain size may have less of a relationship with behavioural repertoire and cognitive capacity than generally assumed, prompting the question of what large brains are for. Larger brains are, at least partly, a consequence of larger neurons that are necessary in large animals due to basic biophysical constraints. They also contain greater replication of neuronal circuits, adding precision to sensory processes, detail to perception, more parallel processing and enlarged storage capacity. Yet, these advantages are unlikely to produce the qualitative shifts in behaviour that are often assumed to accompany increased brain size. Instead, modularity and interconnectivity may be more important.

Conceptual learning by miniature brains

“…It is sometimes assumed that 'simple' and 'miniature' nervous systems such as those of insects implement cognitive faculties by radically different mechanisms compared with vertebrates, rather relying on innate routines and elemental forms of associative learning. However, constructing a great division between simple and advanced nervous systems will lead us astray, because the basic logical structure of the processes underlying spontaneity, decision-making, planning and communication is similar in many respects in big and small brains [11,86].…”

“…Insects have historically fascinated biologists because they offer the possibility of studying sophisticated behaviours [11][12][13][14] and simultaneously accessing the neural bases of such behaviours [15][16][17][18]. Among insects, the honeybee has emerged as a powerful model for the study of associative learning [12,14,15,[19][20][21].…”

Are smaller animals behaviourally limited? Lack of clear constraints in miniature spiders

“…In addition, smaller animals tend to have smaller neurons, and metabolic costs may be relatively higher in smaller neurons. The surface area of a neuron is positively related to its energy consumption (Niven et al 2007), and smaller neurons have proportionally larger surface areas, so comparable informationprocessing capabilities in a smaller brain will result in increased costs due to higher density of metabolic activity (Niven et al 2007;Chittka & Niven 2009). Furthermore, there may also be lower limits on the sizes of functional axons, due to spontaneous opening of voltage-gated ion channels (Faisal et al 2005).…”

“…Intrinsic, adaptive biases in sense organs could in effect perform peripheral pre-analyses of stimuli that would otherwise have to be performed centrally (Fratzl & Barth 2009). The mechanical properties of effector organs could provide partial guidance for otherwise ballistic movements (Seid et al 2008;Chittka & Niven 2009). Greater efficiency could also come from nonspiking interneurons or multifunctional neurons (Chittka & Niven 2009).…”

“…The mechanical properties of effector organs could provide partial guidance for otherwise ballistic movements (Seid et al 2008;Chittka & Niven 2009). Greater efficiency could also come from nonspiking interneurons or multifunctional neurons (Chittka & Niven 2009). The neural tricks hypothesis predicts maintenance of similar behavioural tasks, but perhaps less flexibility in performing them.…”