Sutra 3:9 of Patanjali's yoga sutra states:
The transformation toward total stillness occurs as new latent expressions fostering cessation arise to prevent the activation of distractive stored ones, and moments of stillness begin to permeate consciousness. (Chip Hartranft, 2003).
Exploring the word samskara; Sam = To come together; kara comes from the root 'kud' which means 'to create'. So samskaras are creations, things that we create ourselves. If we think of samskaras as grooves, we can think of our repeated actions chiselling out these grooves, making them deeper, imprinting them deeper into our consciousness, which makes these grooves harder to get out of, harder to fill in.
Samskaras are things that come into being, through a process, through the coming together of actions. If this is the case, then what comes into being can also come apart. What arises can also pass away. All formations created out of conditions are transient, they come and they go. Beliefs too, are samskaras. Beliefs are born out of our conditioned (material) world. Therefore if beliefs are born out of conditions, which are arbitrary and transitory, then it follows that they have no solid foundation and as such can pass as quickly as they were born. Luckily for us, samskaras are transitory, the grooves can be deep, but we can create new grooves and the old grooves over time will infill themselves until they are just a faint scar in our conscious mind, having no hold over us. We all have the innate power to change through practice.
You are not just a brain in a vat!
Thus as Patanjali states, we can create new latent expressions (samskaras) which will stop the old distractive stored ones and total stillness and peace can arise. 'Neurons that fire together, wire together'.
Neuro-plasticity is the core of understanding samskaras; no-one is 'hard-wired', they may have deep samskaras yes, but the brain is plastic and as such can change its structure and function by how we act, re-act, don't act, how we think and how we imagine things. It may just be harder and require more practice to carve out new and healthier neurological pathways. Plasticity exists at every level, the behaviour of the body, of bones, of cells, of thoughts and images. So in yoga we first of all work on the gross body, we change the way it moves, it functions and the more we do this the deeper those changes permeate into the bones, the muscles, the cells, our thoughts and our beliefs. It is even thought it can change on a genetic level, with the possibility of affecting the evolution of the human species.
So we can use our regular practice to re-sculpt our brain, first finding more plasticity in order for it to change, then to create more structure so that new, healthier patterns remain.