According to literature, in case of learning process synaptic plasticity takes place and helps in forming new synaptic connections. what is the anatomical and structural changes takes place in such types of plasticities.
the formation of new synapses is driven by the tendency of neurons to maintain a 'pre-set' electrical activity level. If the average electric activity falls below a certain threshold, the neurons begin to actively build new contact points. These are the basis for new synapses that deliver additional input -- the neuron firing rate increases. This also works the other way round: as soon as the activity level exceeds an upper limit, the number of synaptic connections is reduced to prevent any overexcitation -- the neuron firing rate falls. Similar forms of homeostasis frequently occur in nature, for example in the regulation of body temperature and blood sugar levels.
For a detailed explanation of the anatomical and chemical processes of learning I highly recommend the book, In Search of Memory, by Eric Kantor, who won a Nobel Prize for his work. It is intersting and informative reading.
Learning processes need reverberating processes that make synaptic transmissions happen several times in the circuits that involves in the learning processes. Learning processes also need repeatation. Repeatation of synaptic transmission in any synapse make sensitization of the synapse. Sensitization processes involves the biochemical, anatomical, and genetic processes. These processes lead to the growing of new synapse around neurons that involves in the learning processes.
To George Rozelle: The book "In search of Memory" is indeed highly recommended, but it is by Eric KANDEL (not Kantor). In 2000 Eric Kandel won the Nobel Price for showing learning mechanisms in the Aplysia snail. I also highly recommend watching the film (which tells the same story). Eric Kandel is of Austrian origin but left Austria during the Nazi era. He has also written many textbooks on neuroscience that explain those mechanisms very well. Learing mechanisms in neurons depend on the use of synapses who -via "LTP" (=Long term potentiation)- either become larger or release more neurotransmitters or create additional synaptic connections.