Compared to animals placed in impoverished conditions, animals kept in enriched conditions have been found to have heavier, thicker cortices. this is evidence for

The existence of Brain derived neurotrophic factor (Brain growth factor)

Cortices are the layer of unmyelinated neurons (the grey matter) that covers the surface of the cerebral hemisphere. Brain derived neurotrophic factor (BDNF) are proteins which acts on certain neurons of the central nervous system and the peripheral nervous system. BDNF helps to support the survival of existing neurons, and encourage the growth and differentiation of new neurons and synapses found in the brain and the periphery. For the question given above, the existence of the brain growth factors (BDNF) is responsible for the heavier and thicker cortices possessed by animals kept in enriched conditions.

1: most common garden plants prefer loam — soils with a balance of different-sized mineral particles (approximately 40% sand, 40% silt, and 20% clay) with ample organic matter and pore space. however, some plants grow better in sandy soils, while others are well-adapted to clay soils.

2: available water capacity is the maximum amount of plant available water a soil can provide. it is an indicator of a soil's ability to retain water and make it sufficiently available for plant use. available water capacity is the water held in soil between its field capacity and permanent wilting point.

3: it is the same for all living things (plants and animals). it also includes very tiny organisms that our eyes cannot see. they are known as microorganisms, and include viruses, bacteria and fungi.